TS 2149 
.03 

Copy 1 


^ITED STATES DEPARTMENT OF AGRICULTURE 

BULLETIN No. 681 

Also Bulletin 26 of The Engineering Experiment Station 
The Pennsylvania State College 

Contribution from the Bureau of Chemistry 
CARL L. ALSBERG. Chief 

and the Engineering Experiment Station of The Pennsyirania State CoUege 

R. L. SACKETT, Dean 


Washington, D. C. 


May 18,1918 


GRAIN‘DUST EXPLOSIONS 

INVESTIGATION IN THE EXPERIMENTAL ATTRITION MttL 
AT THE PENNSYLVANIA STATE COLLEGE 


By 


B. W. DEDRICK, Instructor in Milling Engineering, and R. B. FEHR, Assistant 
Professor of Mechanical Engineering, The Pennsylvania State College, 
in collaboration with DAVID J. PRICE, Engineer in Chdrge, Grain- 
Dust Explosion Investigations, Bureau of Chemistry, 

Department of Agriculture 


CONTENTS 


Page 


Page 


Object and Scope of the Investigation 
Principles Underlying Grain-Dust Ex 

plosions.* . . . . 

Apparatus Used in Investigation . . 
Materials Used in Investigation . . 

Experimental Work. 

Experiments from April 6,1916, to Octo 
herS,1917 . 


Discussion of Results and Conclusions . 
Summary of Conclusions . . . . . • 
Appendix: 

Recommendations for Future Inves¬ 
tigations .. • 

Resume of Some Past Explosions . 
Bibliography. 


12 





8 


WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1918 


IKono^aph 

























UNITED STATES DEPARTMENT OF AGRICULTURE 





BULLETIN No. 681 

Also Bulletin 26 of The Engineering Experiment Station, 
The Pennsylvania State College. 


Contribution from the Bureau of Chemistry, CARL L, 
ALSBERG, Chief, 

And the Engineering Experiment Station, The Pennsyl¬ 
vania State College, R. L. SACKETT, Dean. 



Washington, D. C. 


May 18, 1918 


GRAIN-DUST EXPLOSIONS: 


INVESTIGATION IN THE EXPERIMENTAL ATTRITION MILL 
AT THE PENNSYLVANIA STATE COLLEGE.' 


By B. W. Dedrick, Instructor in Milling Engineering, and R. B, Fehr, Assistant 
Professor of Mechanical Engineering, The Pennsylvania State College, in collaboration 
with David J. Price, Engineer in Charge, Grain-Dust Explosion Investigations,' 
Bureau of Chemistry, Department of Agriculture. 


CONTENTS. 



Page. 


Object and scope of the investigation. 1 

Principles underlying grain-dust explosions.. 4 

Apparatus used in investigation. 6 

Materials used in investigation. 10 

Experimental work... 10 

Experiments from April 6, 1916, to October 
3,1917. 12 


■ge. 


Discussion of results and conclusions. 39 

Summary of conclusions. 48 

Appendix: 

Recommendations for future investiga¬ 
tions. 49 

R6sum6 of some past explosions. 49 

Bibliography. 52 


OBJECT AND SCOPE OF THE INVESTIGATION. 

The great loss of life and property resulting from explosions in coal 
mines, flour and feed mills, grain elevators, thrashing separators, etc., 
emphasizes the fact that carbonaceous dusts are very inflammable 
and that careful laboratory and field investigations should be con- 
ducti'd in order to devise means for combating this great danger. 
iUthough Faraday in 1844 suggested that coal dust suspended in air 
would propagate an explosion, it has been recognized only within the 
past 30 years that coal dust is explosive without the presence of 
a combustible gas. And not only coal dust, but many other carbo¬ 
naceous dusts are now knowm to he very inflammable and capable 
of propagating flames. Some idea of the large amount of attention 
that has been given to the explosibility of dusts can be gained by 
referring to the bibliography at the end of this bulletin (p. 52) and 
to tliat printed in Bureau of Mines Bulletin 20, which deals particu¬ 
larly with coal-dust explosions. 


1 The erection of the mill and the conduct of the experiments were under the charge of B. W. Dedrick 
and R. B. Fehr, of the Department of Mechanical Engineering, assisted by P. X. Rice, R. E. Campbell, 
and E. F. Grundhocfler, instructors in experimental engineering, and C. L. Charles, student assistant. 

50220°—18—Bull. G81-1 1 























2 


BULLETIN (581, U. S. DEPARTMENT OF AGRICULTURE. 


Ill June, 191J, an explosion in ii fcH'd-grinding ])bint in BufTalo, 
N. Y., caused the death of J3 men, injured more than 70 emidoyces, 
and damaged a great deal of grain and ])roperty. Shortly afterwards 
the Bureau of Chemistry began its work in connection with dust 
explosions in grain mills, elevators, and industrial ])lants. During 
the period in which this study has been carried on a large number of 
disastrous dust explosions, in which many lives have been lost, 
largo quantities of grain and food products destroyed, and much 
pro])erty damaged, have occurred in grain elevatoi-s, feed, cereal, and 
flour mills, starch factories, sugar refineries, and other industrial 
plants which handle grain. Several definite causes for these explo¬ 
sions have been established, and effective preventive methods have 
been developed and tested. At jiresent the Unitcnl States Depart¬ 
ment of Agriculture is conducting a siiecial war-emergency campaign 
for the ])rcvention of dust explosions and fires. Itepresentativcs of 
the dejiartment are rendering direct assistance to the miUem and 
grain men of the country in installing devices for ])reventing ex¬ 
plosions and in showing them how to remedy dangerous conditions. 

The grain-dust explosion work, as conducted by the Bureau of 
Chemistry, falls into two general classes: 

(1) Dust exiilosions which occur in grain mills, elevators, and 
industrial plants during the handling and milling of grains and the 
manufacture of food products. 

(2) Dust explosions which occur in thrashing machines during the 
operations in the harvest fields. 


MILL AND ELEVATOR EXPLOSIONS. 

As soon as possible after the occurrence of an exjilosion in a mill or 
elevator, the field engineers of the bureau investigate carefully the 
conditions under which the explosion originated and assist the 
company to devise and install some means for preventing any more 
such explosions. During the course of these field investigations it 
has become apparent that one of the causes for a large number of 
dust explosions and fires in the cereal and feed mills, particularly in 
the feed-grinding departments, is the ignition of the dust on the 
interior of the grinding machine during operation. In many 
instances the evidence indicated that the explosion and fire originarted 
within the machine, usually in the attrition type of mill. As they were 
believed to have been caused by sparks from foreign particles or me¬ 
tallic substances entering with the grain, the bureau emphasized the 
necessity for taking steps to remove these materials from the mill 
stream before it entered the grinding machines.^ 


1 Preliminary Report on the Explosibility of Grain Dusts, Cooperative Investigation by Millers Com¬ 
mittee, Buffalo, N. Y., under the direction of Dr. George A. Hulett, chief chemist, Bureau of Mines, U. S. 
Department of the Interior, by David J. Price, engineer in charge, and Harold H. Brown, assistant 
chemist, Grain-Dust Explosion Investigations, Bureau of Chemistry, U. S. Department of Agriculture 
Copies no longer obtainable. . . 









GRAIN-DUST EXPLOSIONS. 


3 


Early in the investigation it became obvious that experimental work 
was necessary to determine the circumstances under which the ex¬ 


plosions and fires might originate and to establish definitely the possible 
causes. Because of the equipment available in connection with its 
milling course and its convenient location to Eastern mills, The 
Pennsylvania State College was selected as the best place for an 
experimental mill. This phase of the dust-explosion work was 
accordingly assigned to the experimental department of that insti¬ 
tution, the experiments being conducted under a cooperative agree¬ 
ment between the Department of Agriculture and The Pennsylvania 
State College. The materials were furnished by various milling 
companies at the request of the department. This bulletin gives a 
description of the equipment of the mill, the manner in which the 
experiments were carried on, and the results obtained, together with 
an outline of conditions conducive to explosions in grinding machines 
and the effect of various preventive devices. 

Aside from the relation of explosions and fires to grinding processes 
in the milling industry, the phase of the grain-dust explosion problem 
discussed in this bulletin, the department engineers have established 
a number of additional possible causes, among which may be men¬ 
tioned: The use of open flames, lanterns, gas jets, etc., defective elec¬ 
trical equipment, frictional electricity produced by friction of pulle 3 "s 
and belts, choke-ups and friction in elevator legs, inefficient methods 
of dust removal and collection, and the continuance of dust rooms. 

Kecent investigations by the bureau have revealed the surprising 
fact that many of the owners and operators of large grain mdls and 
elevators are unfamiliar with the circumstances surrounding grain- 
dust explosions, as a result of which dangerous conditions are per¬ 
mitted to exist. Recently a fire, originating in a dust explosion at 
the top of the elevator leg in one of the lai'ge grain elevators in the 
East, destroyed almost 1,000,000 bushels of grain. The present cri¬ 
sis makes it imperative that all known precautionary methods be 
adopted. The Department of Agriculture is therefore redoubling 
its efforts, and has arranged to conduct a special emergency cam¬ 
paign throughout the United States, to the end that grain dealers 
and millers ma}^ become familiar with the work already" done. The 
field engineers will assist the millers and operators of grain elevators 
in the installation of preventive devices already developed by the 
Bureau of Chemistr^u 


THRASHING-MACHINE EXPLOSIONS. 

The second division of the department’s investigations into the 
matter of grain-dust explosions comprises an extensive study of 
thrashing-machine explosions, which has bc‘en confined largety to 


4 


BULLETFN ()81, U. S. DEPARTMENT OF AGRICULTURE. 


the States of Washington, Idaho, and Oregon.* During the past 
season the investigation has been extended to Colorado, Texas and 
other grain-growing sections. 

THE EXPERIMENTAL ATTRITION MILL. 

The investigations conducted with the exjieriniental attrition mill 
were undertaken for (1) tlie determination of the ])ossii)le causes of 
explosions, and (2) the testing of various jireventive measures that 
have been suggested during the progress of the work. The entire 
scope of the investigation can he seen in the following outline of the 
various phases of the problem that were touched upon: 

1. Sparks emitted by foreign substances. 

2. Naked flame.. 

3. Carbon arc in attrition mill. 

4. Carbon arc in dust room. 

5. Explosibility of various grains.’ 

6. Static electricity in attrition mill. 

7. Static electricity as cause of explosions. 

8. Effect of atmospheric humidity. 

9. Effect of moisture content of materials. 

10. Revolving dampers or fire traps. 

11. Relief valve and pipe. 

PRINCIPLES UNDERLYING GRAIN-DUST EXPLOSIONS. 

On account of the general lack of knowledge concerning the theory 
of dust explosions it may he advisable to insert at this point a brief 
summary of tlie chief facts and principles involved. 

It is generally conceded that two main conditions must he present 
in order that a dust may produce an explosion: (1) Fine, dry dust 
must he in a state of suspension in an atmosphere containing the 
proper amount of oxygen. (2) A source of sufficient heat must be 
brought in contact with the dust. 

It should be noted that carl)onaceous dusts are not considered 
capable of igniting spontaneously, for an outside source of heat is 
required. The following sources of heat have been listed as the 
probable causes of many of the explosions in milling plants throughout 
the country: ^ 

1. Use of open lights, or naked flames, such as lamps, torches, 
gas jets, lanterns, candles, and matches. 

2. Entrance of foreign material in grinding machines. 

3. Electric sparks from motors, fuses, switches, lighting systems. 

4. Static electricity produced by friction of pulleys and belts, 
grinding machines, etc. 

As for the first condition, many factors are involved, such as the 
chemical composition, moisture content, fineness, atmospheric 
humidity, density or degree of diffusion, and presence of inert gases. 


1 U. S. Dept. Agr. Bui. 379. 


* Reference 27, Bibliography. 





GKAm-DUSX EXPLOSIONS. 


5 


The Bureau of Chemistry is now conducting laboratory investiga¬ 
tions of these factors, and has obtained data on the relative inflam¬ 
mabilities of various grain dusts, as well as on the use of inert gases. 
Briefly, the conclusions reached thus far are as follows d 

1. Most of the carbonaceous dusts have a higher degree of inflam- 
' mability than Pittsburgh coal dust. 

2. An inert gas mixture containing 12 per cent or less of oxygen 
will prevent a dust explosion from starting or propagating. 

In 1913 R. V. Mlieeler,^ chief chemist for the Explosion in ]Mines 
Committee, England, published the report of his investigations of 
the relative inflammabilities of various dusts. He classified dusts 
as follows: 


1. Dusts which ignite and propagate flame readily, the source of heat required for 
ignition being comparatively small, for example, a lighted match, 

2. Dusts which are readily ignited, hut which, for the propagation of flame, require 
a source of heat of large size and high temperature, such as an electric arc, or of long 
duration, such as the flame of a Bunsen burner. 

3. Dusts which do not appear to be capable of propagating flame under any condi¬ 
tions likely to obtain in a factory, because they do not readily form a cloud in air, 
or are contaminated with a large quantity of incombustible matter, or the material 
of which they are composed does not burn rapidly enough. 


Class 1. 

Sugar. 

Starch. 

Rice mea. and sugar refuse. 

Wood flour. 

Malt. 

Oat husk. 

Class 2. 

Rice milling. 

Castor oil meal. 

Offal grinding (bran). 

Class S. 

Spice milling. 

Cotton seed. 

Cotton seed and soy bean. 


Grain (flour mill). 
Maize. 

Grain (grain storage). 
Rape seed. 

Corn flour. 

Flour (flour mill). 

Grist milling. 

Corn meal. 

Mustard. 

Sack cleaning. 

Rape seed (Russian). 
Grain cleaning. 


Available data show quite conclusively that tliere is a great simi¬ 
larity between gas and dust explosions. The following extract 
from an article^ by II. II. Brown, of the Bureau of Cliemistry, is of 
interest in this connection: 


It will be noted that just as high pressures have been observed in coal-dust explo¬ 
sions as in gas explosions. However, the extremely high velocities attained by the 
flame in certain gas mixtures have not been reported as observed in dust explosions. 
Such high velocities could not be expected, for even the finest dust jiarticles are many 
times larger than gas molecules, and so, even in the most dense dust clouds, the 
particles could not be as close together nor as intimately mixed with the oxygen as are 
gas molecules. Therefore, the heat of comhustion of one dust particle can not be as 
readily transmitted to the next ])article as it can in a mixture of gases. But the finer 
the dust the more nearly will it approach the-size of a gas molecule. Therefore, it 


1 Keferences 36 and 37, Bibliography. « Reference 26, Bibliograpliy. ^ Reference 36, Bibliography. 





6 


BULLETIN 081^ U. S. DEPARTMENT OF AGRICULTURE. 

might be expected that the velocity of the flame through a cloud of very fine dust 
would more nearly approach the velocity attained in gas explosions. As a matter of 
fact, this is true. Taffanel has brought this out in tests made at the Frencjli Experi¬ 
ment Station. Results obtained by the Rureau of Mines load to the same conclusion. 

The rate at w'hich inflammation travels through a gas mixture is dependent upon 
at least two factors, the inflammability of the gas and the percentage of the gases in 
the mixture. The rate at which inflammation travels through a dust cloud seems to 
be dependent upon two similar factors, namely, the inflammability of the dust and 
the amount of dust in suspension. A thirtl important factor is the fineness of the dust. 

It will be seen, therefore, that gas and dust explosions are similar in many ways, 
and that a gas explosion is only a limited case of a dust ex])losion. 

A thorough knowledge of the nature of dust explosions and of the accompanying 
phenomena is necessary in order to devise means for the prevention of such explosions 
and for the stoppage of explosions if by mischance they should start. It is, therefore, 
necessary to know how dust ignites, the various means by which it may be ignited 
or inflamed, and the chemical processes that take place. Another important factor 
to know is the ease with which the dust ignites and propagates a flame. This property 
we may call the “inflammability” of the dust. The term “explosibility” has also 
been applied in this connection. 

It is important to note that investigations of dust explosions '* 
indicate that, in general, two reports are heard, the first l)eing sharp 
and quick, and the second of a loud, rumbling nature and accom¬ 
panied hy more flame. It is thought that the first report is due to 
the ignition of a small quantity of fine dust in suspension, and that 
the resulting concussion is sufficient to disturl) the dust that has 
settled at places farther away, thus forming an additional explosive 
mixture. The flame from the first explosion furnishes the source of 
ignition for this newly formed dust mixture, so that the liig explosion 
with its loud roar is propagated throughout the entire dust zone. 

APPARATUS USED IN THE INVESTIGATION. 

For the purpose of conducting the experiments on grain-dust 
explosions a small, light frame huilding (15 hy 15 h}^ 24 feet), covered 
witli galvanized iron, was erected hy the Department of AleclianicaF 
Engineering, Pennsylvania State College (PI. I). A small dust room 
was aftenvards huilt at the side of the main structure at the dis¬ 
charge end of the screw conveyor. The grinding floor is elevated 
about 6 feet above the basement, which is level with the ground. 

A 16-inch attrition mill (PL II) was installed on a platform ^14 
inches high, with a removable hopper underneath. Two elevators, 
one dump bin, a stock hopper over the mill, and a small bin for 
receiving ground materials were also provided. A screw conveyor 
10 feet long was placed 2 feet below the floor to receive the material 
from the mill, and to carry it to the chop elevator or out into the 
dust room. The attrition miU, screw conveyor, and elevator are 
driven hy a 15-horsepower direct-current motor, located in the 
basement. 

The elevator legs and feed ])in can he seen on the left of figure 1, 
Plate 11. Immediately over the mill hopj)er are the spouts extend- 


GRAIN-DUST EXPLOSIONS. 


7 


in" down from the stock bin and elevator. The removable hopper 
is partially withdrawn from under the mill platform. Above this 
hopper is one of the steel carbon holders entering the wooden door 
which has replaced the iron door of the lower part of the hood. 
In this wooden door is located a peephole, covered with mica, for the 
purpose of observing any sparks or Hashes that may occur within 
the hood. On the opposite side of the mill (PI. II, fig. 2) is a similar 
arrangement of peephole and carbon holder. The rheostat and 
ammeter for regulating the carbon arc, located on the edge of the 
hopper of the floor dump, are sho^vn on the right. On the floor back 
of these instruments can be seen the recently installed relief pipe (R), 
leading from the hopper to the outside of the building, a distance of 
8 V feet. 

Plate III, figure 1, shows the dust room, located at the end of the 
conveyor, and the small door which gives access to -the basement of 
the mill building. A small box (E) was built over the open end of the 
conveyor for the purpose of inclosing the carbon arc used in Series 4 
(p. 14.) A rehef pipe extends from this box up through the roof, 
and is capped by the hood (F). 

Figure 1 gives a sectional view of the 16-inch attrition mill 
which was used for the tests described in this report. The grinding 



jfiates or disks (d^ and d 2 ) revolve in opposite directions at about 
2,200 revolutions per minute. The upper part of the hood or casing 
(c‘) inclosing the grinding disks can be readily removed. II is the 
feeding hopper where the grain is introduced and fed by a “wabbler,’ 
which is run by the friction pinion on the shaft (f). Horizontal slides 
within the hopper regulate the amount of feed. The adjustment of 
the fineness of grinding is accomplislied l)y handwheels (1 and 2), 
the latter serving as a locking device. The tension spring (ts) holds 






















8 


BULLETIN GSl^ U. S. DEPABTMENT OF AORICULTURE. 


the loft disk in ]:)osition, and acts as a safety appliance to allow the 
disks to separate in case hard substances pass through the mill. 
L is a quick-release lever for operating the spreading device. 

Figure 2 is a diagrammatic view of the removable hopper (h) 

under the mill, spout 
(s), single revolving 
damper (installed for 
Series 8 a'nd 9), and 
screw conveyor. The 
l)y-pass spout with its 
valve -and peephole 
(C) was installed for 
the purpose of observ¬ 
ing how far the flame 
due to an explosion 
may be propagated 
without the use of a 
check” valve. B is 
a peephole for observ¬ 
ing any flames that 
may pass the damper. 
The construction of the single damper can he seen in figure 3, 
which gives the arrangement when two of these single dampers were 



Fig. 2. 


-Elevation-attrition mill and conveyor. 
Single damper. 



placed in series, as in Series 11. As can ])e seen in the sectional view, 
the paddles or blades with their rubber 'Svij^ers,” shown in black, 
are so arranged that there is never a clear i)ath through the damper. 






































































































Bui. 681, U. S. Dept, of Agriculture 


Platc I 



Fig. 1. 



Fig. 2. 

Exterior of Experimental Mill Building 













































Bui. 681, U. S. Dept, of Agriculture. 


Plate II 



Fig. 1. 



Fig. 2. 

Interior of Experimental Mill Building, 







Bui. 681, U. S. Dept, of Agriculture. 


Plate 111 



Fig. 1.—Dust Room, 



Fig. 2.—Removable Hopper 



















Bui. 681, U. S. Dept, of Agriculture 


Plate IV 




Fig. 2.—Interior of Basement, 










GRAIN-DUST EXPLOSIONS. 


9 


In figure 4, which is a diagi’ammatic view of the double damper 
and principal parts of the mill equipment, it is seen that the conveyor 
was lowered aliout 10 inches in order to make room for the doid)le 
damper. Otherwise, the arrangement is practically the same as that 
in figure 2. The relief valve at A was installed with the relief pipe 



as explained in Series 13 (p. 18). The ^^spout to elevator,” with its 
slide under the screw conveyor, shoVvs how the gi-ound material could 
be ^^recirculated,” as stated in several series of tests, by means of the 
elevator and spouts shown in Plate II, figure 1. 

Idle two dampers were positively connected with each other by 
means of a chain and sprocket wheels (fig. 3) and were so ari-anged 
that they served as a double check for the fiame })ropagated by explo¬ 
sion in the attrition mill. Plato IV gives two views of this double 
, damper from opposite sides, figure 2 of the plate showing also the 
screw conveyor, peepholes, and spout leading to the boot of the meal ' 
or chop elevator. 

Plate III, figure 2, shows the removable hopjier, with the sheet- 
iron liidng and swinging relief valve as installed for Series 13. This 
hopiier was constructed so as to make a snug fit with the lower })art 
of tlie hood of the attrition mill. When the hopper is in ])osition 
under the attrition mill, the relief pipe (R) (PI. II, fig. 2) can be at¬ 
tached to the stub spout containing the relief valve. 

50220**—18—Bull. G81-2 













































































































10 BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 

I 

Plate 1 shows the })uirs of smoke, dust, and charred particles that 
followed a llame issuing from the end (G) of the relief pipe when an 
explosion occurred in the attrition mill (Series 13). 


MATERIALS USED IN THE INVESTIGATION. 


DESIG¬ 

NATION. 

NAME. 

% 

DESCRIPTION. 

A. 

Fine oat hulls. 

Oat hulls, finely ground in an attrition mill, millstone, or other grinding 
mill. 

B. 

Elevator dust. 

Dust thathassettled on machines, beams, etc., in a grain elevator. It is 
a highly inflammable dust of a very light and line texture, and com¬ 
posed of floating carbonaceous material of grain, outer skins, together 
with foreign dust. 

C. 

Oat hulls. 

The hulls stripped from oats, as in the preparation of oatmeal. 

The interior or endosperm of any grain reduced to a very fine powdery 
state and free from the branny covering. It is composed mostly of 
starch, and is highly inflammable when in suspension. 

i)i. 

Flour direct from 
store. 

1).,. 

Flour (oven dried).... 

Flour dried in an oven at about 150® F. 

j:. 

(jlraham flour. 

This is wheat which is ground but not bolted. It contains all of the 
flour, bran, and germy parts. 

A flufTy and inflammable dust taken from dust collectors which are con-, 
nccted to the scouring or brush machines. It consists of foreign matf- 
rials, such as dirt, smut, and portions of the light, thin, and loose outer 
skins of the bran. 

F. 

Wheat scourings. 

(;. 

('orn. 

Shelled com. 

II. 

Wheat shorts. 

Composed of the finer portions of bran, germ, and some floury material, 
separated from flour, in the process of milling. 

I. 

Coarse floor sweepings 

A coarser mill dust, settling on floor in immediate vicinity of mill. 

j. 

Fine floor sweepings... 

The lighter and finer mill dust which settles in the room and outside the 
immediate vicinity of the attrition mill. 

K. 

Conveyor mixture. 

A mixture of various materials as obtained from the end of the screw con¬ 
veyor. 

L. 

No. 2 feed dust. 

Consists of very fine particles of bran, fuzz, smut dast, and dirt, taken 
from the dust collector which draws air from the first scourer. 

I.I. 

No. 1 feed dust. 

A material taken from the dust collector drawing the air through the 
second scourer. It consists almost entirely of the outer layers of the 
bran which have been removed by the scouring action of beaters. 

N. 

I^ine oat hull dust. 

This material is very finely ground oat hulls, brought out by the con¬ 
veyor in the form of dust. 

o. 

No. 3 elevator dust... 

Floating dust gathered by hand from the beams and machinery in the 
elevator. 

r. 

Barley malt sprouts... 

Consists of barley malt sprouts that have been used as mash material and 
then dried. 

Q. 

Malt sprouts. 

Consists of the radicles grown on the barley during the germinating proc¬ 
ess, and later broken off and dried. 

II. 

Brewers’ dried grain.. 

This is the residue from a mash tub in a brewery or distillery, and con¬ 
sists of malt, com, rice, hops, etc., which have been boiled and then 
dried. 

s. 

Dried grain. 

This corresponds to “brewers’ dried grain,” except that the original 
mash consists of corn, barley, malt, and the radicles grown on barley 
during the germinating process, which are later broken oil and dried. 

* 


EXPERIMENTAL WORK. 

The results of the investigation are reported, first, by describing 
and summarizing briefly each one of the experiments performed, and, 
second, by discussing each one of the factors mentioned in the scope 
of the work (p. 12). 

PRELIMINARY TESTS. 

The experimental mill building at Tlie Pennsylvania State College 
was completed in the spring of 1915, and the attrition miU, elevators, 
and conveyor were installed during the early part of the summer. 
During August several preliminary experiments were made for the 
primary ])ui-pose of ascertaining if explosions would result from the 
s[)arks emitted by foreign materials (nails, flint, matclies, etc.) when 
]){issing between tlie grinding disks along with tlie grain. 
















































GRAIN-DUST EXPLOSIONS. 


11 


At first the hood of the attrition mill Was removed, so that the 
sparks emitted could he o])served. AVlien a single nail (eightpenny, 
but clipped to a length of about one-half inch) or small piece of stone 
was passed through the mill, sparks were, in nearly eveiy case, 
emitted from different points of the periphery of the disks. Feeding 
1 to 2 ounces of tliese clipped nails, small pieces of flint, or otlier hard 
materials, either singly or in combination, resulted in a large number 
of sparks, as in the case of an emery wheel. These sparks were thrown 
a distance of from 10 to 16 inches from the periphery of the disks. 
The sparks were emitted radially when l)oth discs were running, and 
tangentially when one disk was stationary. •Wien matches were fed 
into the mill, usually no sparks were emitted from the periphery of 
the disc, as the rapidly revolving arms of the disk generall}^ ignited 
the matches before they had fairly entered the eye of the runner. 

. After making these observations of the sparks produced by foreign 
materials passing through the attrition mill, the hood was replaced, 
so that various kinds of grain products could he fed into the mill, 
with pieces of flint, nails, matches, etc. Three to five quarts of oat 
huUs, corn, elevator dust, flour, wheat scourings, wheat shorts, and 
floor sweepings were fed into the miU, at first singly, then in various 
combinations, with about 2 ounces of foreign materials, a cpiantity 
which probably would greatly exceed the amount of such materials 
finding their way into an attrition mill witli the grain during a com¬ 
paratively long period, under ordinary milling conditions. The 
disks were set very close in order to grind as fine as or even finer than 
is usual. Kepeated attempts with such materials as flour, dried ele¬ 
vator dust, and dust settlings failed to produce a single explosion. 
Further efforts were made to obtain explosions by duplicating, as 
far as possible, the actual conditions obtaining in an attrition mill, by 
feeding the grain at normal rate until several bagfuls had been passed 
tlu’ough. At frequent intervals pieces of nails, flint, etc., were added 
with the grain, but never was there the slightest evidence of an 
explosion. 

The first explosion in the experimental attrition mill was obtained 
shortly after the preceding series of runs at the time when J. K. 
Clement, of the Bureau of Mines, was present to witness the tests. 
The bottom of the hopper was closed hy the slide so as to retain the 
ground material and not permit any dust to escape except through 
the hand hole, winch was open. Wlien a quantity of elevator dust 
and ground oat hulls was fed into the mill, a rather dense cloud of 
dust issued from the hand hole, due to the fan-like action of the grind¬ 
ing disks. Upon })lacing a gasoline ])low torch near this hand liole, 
the dust ignited and a flame, 6 feet long, shot out toward the wall, 
llie ho])])er was immediately withdrawn, and about a (piart of the 
same matei’ials thrown into the mill, while the torch was introduced 


12 


BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 


just Avitliiii the space previously occupied by the liopper. A very 
thick cloud of dust was l)lowii into the room. Immediately an 
explosion, or rather a large llame, occurred, followed by a second and 
more extensive one, covering nearly all the floor area of the dusty 
side of the buildin" and extending almost to the roof. The door and 
windows were open. Otherwise, some damage might have resulted. 
As it was, the arms of tlie man who handled the torch were burned. 

The results of these ])reliminary experiments (observed by J. K. 
Clement, B. AV. Dedrick, M. P. llelman, J. Weaver, and F. Kline), 

mav be summarized as follows: . 

« 

1. More than 40 attempts with a total of from 3 to 5 pounds of 
foreign materials, sucli as nails, small pieces of stone and flint, and 
matches, fed along with various kinds of explosive grain products, 
failed to jiroduce a single explosion. 

2. Two attempts with a naked flame were successful in ])roducing 
explosions. 

EXPERIMENTS FROM APRIL 6, 1916, TO OCTOBER 3, 1917. 

SERIES 1. 

Object .—The object of the test was to determine whether explosions 
could be obtained by foreign materials capable of emitting sparks 
when ground, or by an electric arc located near the disks of the 
attrition mill. 

Cond'dcons .—The two removable iron doors of the mill were replaced 
by wooden doors, provided with peepholes covered with several 
layers of mica, and drilled for the insertion of iron carbon holders for 
the electric arc. The position of the arc could be shifted between the 
shaft and periphery of the disks, ])ut it was soon found that its location 
did not seem to have any effect on the regularity of the explosions. 
As a rule, in this and succeeding tests, the arc was located nearer the 
shaft than the periphery. A rheostat and ammeter were provided for 
regulating the current (usually 15 to 20 amperes) througli the arc. 
Tlic liopper underneath the grinding disks was put in place, and its 
hand liole was left open so that the flash due to an explosion could be 
seen. 

Resulis .— 

1. Sparks from foreign materials did not cause an explosion. * 

2. Tlie electric arc caused four explosions out of six attempts when 
large handfuls of feed AVere used. 

3. Low rates of feeding did not produce an explosion with the 
electric arc. 

4. Oat liulls, ground or unground, dhl not ignite, except when 
mixed with the higldy inflammable elevator dust. 

5. With elevator dust, when fed by the handful, either alone or 
with oat hulls, four explosions out of four attempts were obtained. 


GKAIN-DUST EXPLOSIONS. 


13 


SERIES 2. 

Ohjcct. —Same as that of Series 1. 

Conditions. —Similar to those of Series 1, except that one of the 
disks was ])locked so as to permit foreign substances, su(*li as nails, to 
he in longer contact with the revolving disk and thus to give off more 
sparks. Definite amounts, usually 1 pint, of feed were measured out 
for the purpose of determining the limits of explosibilit}^ of various 
mixtures. 

Rpsults .— 

1. In 21 attempts with the electric arc and vaiious grains and 
mixtures, 16 explosions were obtained. 

2. A mixture of 1 part elevator dust to about 8 parts of oat hulls 
appeared to be the limit of explosibility of tliese grain products. 

3. "VMien there was no opening the explosion was propagated to the 
outside end of the screw conveyor, as indicated by puffs of smoke 
(E in PI. Ill, fig. 1, and in fig. 4). 

4. Blocking one disk appeared to give results not different from 
tliose obtained when both disks were running. 

5. Other results corrol)orated those of Series 1. 

SERIES 3. 

Object. —The primary object was to determine how far the flame 
was propagated from the source of the explosion. 

Conditions. —The conditions of the test were similar to those of 
Series 2 (one disk being blocked), but the humidity was very high, 
inasmuch as there was a steady rain during a large part of the test. 
A 4 by 4 inch hole was cut in the upper part of the horizontal screw 
conveyor, about 1 foot from the chute leading down from the attri¬ 
tion miU and about 5 feet 4 inches from the shaft of the mill. The 
various kinds and mixtures of feed were prepared and measured 
into small paper bags, the contents of one of which were dumped 
into the feeding hopper at each attempt. 

Results .— 

1. Out of 39 attempts with the electric arc, 36 explosions occurred, 
in spite of the very damp atmosphere. 

2. Explosions were obtained with elevator dust ajid oat huUs, and 
elevator dust, flour, graham flour, wheat scourings, floor sweepings, 
corn, and various mixtures of these substances. 

3. The following classification of the 36 explosions may be made 
(PI. Ill, fig. 1, and text fig. 2): 

27 flashes were observed at B (5 feet 4 inches from shaft of mill). 

9 flames were observed at E (12 feet 6 inches from shaft of mill). 

3 flames were observed at F (17 feet from shaft of mill). 

4. Duriiiir the course of the tests the convevor continuaUv brought 
out smoldering lumps of ground products, which could be readily 
fanned into a red glow. 


14 


BULLETIN G81, U. S. DEJ'ARTMENT OF AGIMCULTUKE. 


SERIES 4. 

Object .—^Tlie object' of this series of tests was to attemj^t to ob¬ 
tain an explosion in the dust room (located outside the building, 
at the end of the screw conveyor) and to determine if such explosion 
would propagate the flame back to the mill. 

Conditions .—This dust room (5 by 10 feet by 7 feet high) was 
made as tight as possible, and the door was replaced by a heavy 
muslin curtain to retain the dust, at the same time permitting free 
expansion in case of an explosion. The electric arc was located at 
first in a small box built above the end of the conveyor, and later 
just outside this box. In both cases the arc was regulated by means 
of a long wooden pole extending to a safe point outside the building. 
The duct leading from E to the vent at F was removed (PI. Ill, fig. 1). 
The hopper was placed under the grinding disks, and aU holes, in¬ 
cluding B, were closed, in order to retain the dust as far as possible. 
Both disks of the attrition mill were run at their normal speed of 
2,200 revolutions per minute. The arc was turned on, and various 
kinds of grain products, which had given explosions in previous 
tests, were run through the mill as rapidly as possible in order to get a 
large amount of dust into the dust room. After various grains had 
been fed for 15 minutes, a blast of burning dust was observed issuing 
from the outlet in the box above the conveyor. It was evident 
that the rapidly revolving attrition mill produced enough draft to 
force its dust out at the conveyor end without the use of a special 
fan. In fact, the force of the blast was so great that it did not ap¬ 
pear possible for the flame to get back to the attrition miU. The 
flame was extinguished by merely turning off the arc, and then more 
elevator dust was rapidly fed into the mill, the arc having been 
turned on again. Within 2 minutes, another heavy blast of flame 
was observed at the end of the conveyor. In this instance the flame 
could not be extinguished by turning off the arc, because the wooden 
box on the end of the conveyor had caught fire. The mill was 
stopped immediately, and the burning box saved by means of a fire 
extinguisher. After the arc had been placed just outside this box 
the miU was run again. Elevator dust and ground oat hulls were 
fed for 15 minutes, during which time the room became very dense 
with dust. Although the arc had been burning during this time, no 
explosion occurred, but, as before, due to the intense heat radiating 
from the air, the box over the end of the conveyor was again on fire. 
The miU was stopped, and the fire easily extinguished with a pail of 
water. 

Results .—No explosions were obtained in the dust room by means 
of an electric arc in this series of tests. 


GRAIN-DUST EXPLOSIONS. 


15 


SERIES 5. 

Object .—This test was run as a demonstration to Government 
officials from the Bureau of "Mines (G. A. Hulett and J. K. Clement) 
and from the Bureau of Chemistry (1). J. Price, IT. IT. Brovm, and W. 
G. Goodenow). 

Conditions .—The arc was located near the disks, which were run at 
their normal speed. Various kinds of grain products (except ele¬ 
vator dust, the supply of which had been exhausted) were fed mto 
the attrition mill. 

Results .—^Vlthough explosions were readily obtained with flour and 
wheat scourings, none was obtained with corn, as in Series 3. In 
fact, the regularity and force of the explosions, none of which caused 
the flame to extend as far as the end (E) (PL III, fig. 1) of the conveyor, 
were not nearly as great as in Series 3, in spite of the relatively low 
humidity (49 per cent) of Series 5, as compared with other tests. 

SERIES 6 AND 7. 

Object .—These experiments were run to determine whether an 
explosion would result from the discharge of static electricity. 

Conditions .—^The conditions of testing were similar to those of 
previous tests with the electric arc. The carbons were replaced by 
. |-inch brass baUs screwed on the ends of long f-inch iron rods, which 
replaced the f-inch iron carbon holders. These f-inch rods were in¬ 
serted through porcelains in the wooden door of the hood, to insure 
insulation from the metal frame of the machine, and were comiected 
by 15-foot leads to the poles of a small Wimshurst machine. 

Results .—Under normal conditions this machine ^yas capable of 
producing a good spark about 3 inches long, but under the condi- 
’ tions of the test, with the long leads, and great leakage, it gave only 
a very weak spark, hardly more than 4 inch long, between the brass 
knobs near the disks of the mill. It was, therefore, decided to make 
use of an induction coil instead of the static machine. By this 
means a very hot and almost continuous spark 2 inches long could 
be obtained between the brass knobs. On two different days a total 
of 20 attempts was made to obtain explosions with various inflam¬ 
mable dusts by means of the spark from an induction coil. The 
spark gap was varied from J to If inches. No explosions occurred. 
This negative result, of course, does not indicate that static electricity 
can not cause an explosion in an attrition mill, but rather that un¬ 
der the particular conditions of the test, the mixtures of air and dust 
were not sufficiently inflammable to be ignited by the sparks from an 
induction coil. In order to show that the electric arc, on account of 
the greater amount and intensity of heat produced, could ignite 
the same mixtures under the same conditions, the carbons were 
quickly substituted for the brass knobs, and then within 10 minutes 


10 BULLETIN 081, U. S. DEPARTMENT OF AGRICULTURE. 

of Series 7, a number of explosions was obtained in Series 8 with the 
same substances by means of the electric arc. 

SERIES 8 AND 9. 

Object .—The object of these tests was to note the effect of a single 
revolving damper in preventing the ])ropagation of exjdosions 
occurring in an attrition mill. 

Conditions .—The revolving damper was installed as shown in 
figure 2. The details of this damper may be seen in figure 3, which 
shows two such dampers in series. The by-pass and .butterfly 
valve were inserted to make certain that the flame would be propa¬ 
gated that far when the damper was off, or out of service. 


Results .— 

1. Total number of attempts to obtain explosions with arc. 73 

2. Total number of explosions. .. 57 

3. Damper in service during explosion. 29 

4. Damper out of service during explosion. 28 

5. Flashes of flame in by-pass (damper off). 11. 

6. Flashes of flame at end of conveyor (damper on or off). 0 

7. Puffs of smoke at end of conveyor (damper off). 21 

8. Flashes of flame past damper when in service. 6 

9. Puffs of smoke at end of conveyor (damper on). 0 


SERIES 10, 

Object. —To determine whether static electricity was built up 
during the operation of an attrition mill. 

Conditions. —For this purpose a sensitive gold-leaf electroscope was 
procured from the Department of Physics. The collecting devices con¬ 
sisted of a comb made up of pins and tin foil located near one of the 
driving belts and of two 5-foot flexible lamp cords with 3-inch pieces 
of No. 14 bare copper wire soldered to each end. During the tests 
the casing of the electroscope was grounded by being hold in the 
hand, while the binding part of the gold leaf was connected by the 
'flexible wire lead to the collecting' comb, or any part where it was 
desired to test for static electricity. The attrition mill was run 
at its normal speed cf 2,200 revolutions per minute. 

Results.- —See Table 10, page 29. 

SERIES 11. 

Object. —To note the effect of a double damper in preventing the 
propagation of explosions. 

Conditions. —The single damper used in Series 8 and 9 seemed 
to retard to a marked degree the propagation of explosions occur¬ 
ring in the attrition mill, but did not always prevent the flame 
from getting past the clamper. Consequently, a double damper 
(figs. 3 and 4 and PI. IV) was installed, with a view to checking 
any flame that might pass the first set of revolving paddles. Inci- 











GEAIX-DUST EXPLOSIONS. 


17 


dt'ulally the mill was run several hours while oat hulls were fed 
at as great a rate as possible. The ground oat hulls were eoiiveyed 
back into the mill in order to produce as much dust as jiossible. 
For over an hour the electric arc was turned on, but not a single 
explosion resulted. 

Results .— 

1. During the operation of the attrition mill under severe con¬ 
ditions as to rate of feeding and source of ignition no explosion 
could be obtained with oat hulls during a period of over an hour. 

2. Out of six explosions with the dampers in service two flames 
shot past B and D (tig. 4). 

3. In two instances with the dampers in seiwice smoke was 
observed issuing from the end of the conveyor, but without any 
force. 

SERIES 12. 

Object .—Same as that of Series 11. 

Conditions .—Similar to those of Series. 11, except that the oat 
hulls used during the jirelirninary run had lieen fairly wc'U dried 
by being spread out in shallow jians, which were then ])laced on top 
of radiatoi-s for a period of several days. Thus the moisture content 
was reduced from 9.9 to 3.2 and 5.7 per cent. 

Results .— ■ 

1. Only one explosion was obtained during the continuous grind- 
mg of fine oat hulls. 

2. In each of the four explosions with the double damper in 
service a flame got past the damper and in three cases extended 
as far as D. 

3. In no instance was a flame observed at the end of the con¬ 
veyor. 

4. Smoldering lumps of ground products were found to be very 
dangerous, in that they set fire to the wooden base of the attrition 
miU. 

On account of the fire hazard involved in these smoldering lumps 
of grain, special emphasis should be placed on this result of Series 12. 
During this scries of tests it was observed that smoldering lumps, 
resulthig from the explosions, were frequently brought out by the 
screw conveyor. Some of these lumps happened to be placed on 
several layers of asbestos paper. After several minutes it was ob¬ 
served that a hole had been burned through the asbestos paper. 
Even when this smolderhig material was buried under several inches 
of grain it continued to burn, although not as well as when it was 
spread out in a thin layer and exposed to the atmosphere. That this 
smoldering material was to be regarded as a great source of danger 
was very forcibly demonstrated when on the following morning it 
50220°—18—Bull. G81-3 




18 


BULLETIN 081^ U. S. DEPARTMENT OF ACJRICULTURE. 

was (liscovored tliat the wooden ])latform and floor near tlie remov¬ 
able hopper of the attrition mill had been set on fire, evidently by 
some smoldering grain that had not been removed after the experi¬ 
ments of the preceding day. This result strongly suggests a greater 
use of sheet iron, or other noncomhustiblc material, in milling 
plants. 

SERIES 13. 

Object .—The object of this experiment was to note the effect 
of a pressure-relief pipe. 

Conditions .—It had been suggested that a means for automatically 
reheviug the pressure, due to an explosion, might aid materially 
in preventing the propagation of the flame to a dangerous part of 
the miU. Accordingly, a device (PI. II, fig. 2, and PI. I, fig. 1) 
consisting of a pipe 5 inches in diameter and feet long, with a 
rectangular end containing a light sheet-iron rehef valve, which 
remained closed by its method of overhead suspension (fig. 3), was 
installed. This end of the relief pipe was inserted in the hopper 
(PI. Ill, fig. 2), which had been lined with galvanized iron on account 
of the many fires that had occurred in the wooden hopper. 

Results .— 

1. In nearly all of the 14 explosions with the damper in service 
a llame and puff of smoke were observed at the end of the relief 
pipe (G), indicating that the relief valve opened properly. 

2. In four out of eight instances, however, flames were observed 
getting past the double damper, although never as far as the con¬ 
veyor end. 

SERIES 14 AND 15. 

Object .—The primary object of these last experiments was to 
determine whether certain grain products, such as oat hulls, con¬ 
taining considerable dust, barley malt sprouts, malt sprouts, brewers’ 
dried grain, and ‘‘dried grain,” aU of which had been recently re¬ 
ceived from various manufacturers, would give an explosion under 

severe conditions in an attrition mill. Incidentallv, observations 

%/ ' 

were made of the effects due to the relief pipe and double damper. 

Results .— 

1. By means of the electric arc, explosions were obtained with 
dusty oat huUs, malt sprouts, barley malt sprouts, brewers’ dried 
grains, and various mixtures (Table 16). 

2. Out of 45 explosions with the damper in service, four flames 
passed the damper, one of them extendmg as far as the end of the screw 
conveyor. 

3. In all cases of explosions, puffs of smoke were observed at the 
end (G) of the relief pipe (PL I, fig. 1). 


TABULAR STATEMENT OF RESULTS OBTAINED AT THE ATTRITION MILL. 


GHAIN-DUST EXPLOSIONS. 


m 


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IMte: April 6,1916. 

Weather: Cloudy, but bright; no wind; 51® F. 

Observers: R. L, Sackett, B. W. Dedrick, R. B. Fehr, B. J. Culp, H. R. Brown. 



































































20 


BULLETIN G81, U. S. DEPARTMENT OF AORICULTURE. 


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X 

X 

X 

• 

• 0 

0 

1 

>> 

1 

1 

» 

• 


1 


•p4 



1 cZ • 

• > 

4J 

CZ 

> 

1 

(O 

!i2 2.2 

1 

• 

a,2 

a^q 

t 

1 

1 

• 

a^q 

a^q 

a,2 

• 

• 

• 

1 

> 

d 


‘O':: I 


:: ‘r: 3 3 


>'2 

u O 

Q (>4 


u 


p^o (-0 ; p,0 p,0 


cc 


a 


. O O ‘O o 

• 00000 

O ^ ^ ?H 


o 


f »o 


40 o 

C^l CO 


10 


CO 


o 

CO 


CO 

ft 


3 

_o 

•to 

CO ft 
3 i*) 
3 3 

p 

ftla 


o 

33 


bo 

.a 

•4^ 

O 

2 ; 


CO 

3 

o 

OT 

o 

ft 

3 


O O 

33 


o 

<1 


000 

333 


c« 

3 

3 

(m 


3 

o 


o 

d 

o 

u 

04 

Ui 

o 


O CO 

40 ^ 

. . 3 

CO OT 2 
3 3® 


^ 'ft 

i'2.s3.a«.a3"= 

G 

3 

4^ 

.a 

fS 

^..a 

® p ft 

a a-s 

; ; ft® (po p,® 


ft 

ft 

; ft 

3 3 fp 

1 • 1-H 4H 4H 

• I 


4H 

4H 

* tH 
( 

CCCQ.-I 

- X 05 0 ; 




CO ^ 

10 CO I 

• 

• 

( 

1 

1 

• 


4^ 

rH 

tH 1-H 

1 

4H 4H • 

• 

• 

• 


ft 

a 

a> 

4<d 

c3 

OI 


40 

CO 


OC O CO 
CO ’-r 


CO 


o 


00 


000 


Sr;? 13 

000 


00 

10 


c o 


O CO >0 


3 3 

la 

CQ 


3 

jQ . 

"o ’ 

O 

a 

a 

<0 

-ft 

ft 

a 

3 

ft 

ft 

ft 

3 " 

o 

1- 

ft 

ft' 

a 

ft 

I—H 

3 

ft 

»-» 

ft 

t-T 

■3 

3 

r 

ft . 

CO 

. -I—( 

3 -. 
3 

« 

• 3 ® 

’ ^P\ 

05 ‘-T • 

« 2 • 
- ®a 
•• 

S • • w 
-< £ ?> 
• •T3 >-* 

c«, ,0 

fi?o 


CO 

































































































































Table 3. —Scries 3. Flame propagation. 


I 


GRAIN-DUST EXPLOSIONS. 


21 



^JL 

t^X^ . 

4-» 




6 


•§ S 2 

2 2 0 

3 

■ rO 






fc- ^ 

fe 

Ui 

*3 




o 

>3 

CO 

a , c. 

CH 

o 

o 



C 

2 

f-4 

2 

00 

o . 

r2 

4-> 

O 


• 

tH 

<44 

O 

a 

o 

lO ^ 
^ CO o 
22 

S'© g 

2 

gl 

fcjo 

o 

4^ 

44 

O 


o 

4-> 

o 

U) 

o 

44 

2 

o 

[o 


ft ft.a 

ftft 

2 o 

d 

44 

X 


<v'^'~' 
C >3 

o 

ft's 

CO n 

ft 

CO 

M 

44 

CO 


4.> 

cc 

ft -S 

UlUl 

CO 

•rH 

P-1 


CO 

Pm 

C 

l«H 


c3 


g§ 

O >i 

c/i O 


S ^ 

S 

Eh 

o •v 

1I& 

-l-> 

U1 


'l-d 

o 

'O 

c3 


O 

•M 

C3 

o 

a 

C3 


!/; 

C 

O 


f-i 

CO 

o 


w 


M 


!3 

S 

Ph 



• • 

:ft‘ : 

t a 

• a 

:sc 

; C 


SC 

c 

••I'i 

CO 

2 

Pm 

:pmPm 

■ Pm 

E 


pi. 


o 

73 






« 

3! 


O 

'C 


d ® o o 
'O'glJ'Ci 

a 

m 


o 
o 

a 

“ o 
•g-o 

3! 

v-i 

r'i 


d g d 

a-^ a 
.2 

Pm CO Pm 


o o 
'O'C 


o o o o 
'O'O'O'O 


o o o o o 
*td *o ^ 


w 

3 


h-S b 

c3 C3 
O O O O 

>k;^w 


sc 


Stt 

s 

ft 

4-3 , 

-^^sa 

.EJC 

hPIPi. 


o o o o 
'd’d'C'C 


o 

«C3 

C 
o 

S-H 
Ol 

ft 
ft 
o o o 


"C 'O a3 


a| : 

^ ^ s 

«ca-g 


bC 


o a 

CO 


o 

• r-* ^ 

»--iB - 

>2 5=! M 

COftlZiPM 


SC 
4^d5 

coPi. 


bJD 

O.S O 
'CaJ'O 

* -4-^ 

O 


© 


'sS'a 

PnWPk 


bO 

a 


® d d ® 
-K c-o-^ 
o o 

ai2 

CO Pm 


a 

CO 


_ o o o 

'P'C'C'O 

v/j 

p2 

Pm 


C3 

ft 

ft 

fl 

03 

SC 


2 ft ftft 
bo 


O 

ft 


o 

;zi 


PQ 


C 

o 


c 

bo 


© 

l-H 

C 


o o o 
ft ft ft 


o 

ft 


o o 
ftft 


OOOO OOOOO i : ioo 
ftftftft 'o'a ft ft ft'ftft 
.C ft d • • 

ft 03 t. 


pm;z;<) 


o 'O 

•M 

c3 


o 

Ui 

<5 


coo 


'V 

o 

o 

Ph 


c/2 

2 

nd 

tH 

o 

c3 

a 

■p. 


2 

'O 

u 

o 

•4^ 

c3 

o 

'o 

o 

2 


2 

xf 

O 

•4-d 

> 
o 

'o 

^ftft c^ 


X CO ><! CO 

H’c a^ 

ft ft 


c 

o 

ft 

a 

d 


■ §'3 

Sft M 


C C 


c3 


§ 

a 

o 

ft 

© 

a 

1 


M 

tx, 

a 

Uh 

§ 

O 

CO 

4^ 

c3 

O 


c 

52 


4^^ 4^_ 


CO 

2 

T? 

o 

"*-> 

2 

> 

O 

13 

TJ 

§ 

s 

o 

o 

o 

u. 

2 


4 fl d 

P-o o 

'co''^ 


PJ 


cc 


~ C -C 
ftc3 P-CS ftp. 


O O o o o o o 

pftft ps-pft pftftftft 
•—< • • O ... 

ft • • ft4J ft • ft 


ic COt^ OOOOt-i MfOTfiOCO 


c 

a’^ 


CO 

2 

no 

O 

4J 

d 

> 

o 

o 

2 

c3 

2 

u 

O 

o 

o 

u. 

2 

X 

a 

IN 


t^CJOO) 


CO 

2 

Ui 

o 

4^ 

C3 
O 

13 

2 
2 
2 

0+^0 
0^0 

(h ^ U 
2 fc- 2 

-M c 

^ o 

■§>a'^eS 

O , c o 

r-l ^ 1-4 I O 

.oPh 


S-, 

O 

4-d 

2 

O 

'3 

T3 

2 

2 

2 


CO 

2 

'O 

t-i 

O 

4-> 

2 

> 

o 

13 

xf 

2 

2 

•> 

a 

o 

© 


O I-M (N CO 
N IN IN C^l 


© 

a 


.>o 


cc CO iS S o o ift 
oi 03 03 o' O O O 


O IN 

r-H 

od 


Tji CO o 

»-H f-4 


'H^COr^OOOC^‘OcO< 

<NC''»C^<NCOCOCOCO< 


) OMO 
) CO Tf« 


OOOO ooooooooooo 


Q {N CO »0 CO (N 

iC »0 »0 ‘O ‘O o 
d d d d d ^ 









































































































































































Table 3 .—Series 3. Flame propagation —Continued. 


22 


BULLETIN' U. S. DEPARTMENT OP AORTCTU.TTTRE. 


w 

c3 

a 

<a> 


o 

D 

2 

o 

p- 

a 

o 

o 

(A 

P 

O 


o 

3 

'O 

Ih 

O 

O. 

o 

C3 

<X> 

a 

c3 


P^t 

-4^ 

CC 

o 

a 


a 

<» 

■«.> 

<v 

'd 


Oo 

(N 

d o 

ai 

CQ 


i 

•F^ 

"S 

i: 

a> 

tn 

Xi 

O 


W 


d 

o 


d 

to 


•d 

(V 

0 / 


d X 

p. o>5 

H 


a 


® o 

-g-d 

a 

OQ 


OT ^ 
C3 


t£ 

.3 

5 = 


o ; : o 

a ' a 

g d ^ c 

^ C3 

O 

a •- 

M :« 


o o 
o 

a 

CQ 


o.w'3 


dodo 

'd'd'd'd 


Ph 


* * ' ^ 

' O * C S * I * ri ' O 

I T5 iP ^ i-C • {/> 'O 

! . c3 . o • 

:z;i^p^fxHc^PLH ’ 


t * 

• • 

» • 

• • 

« > 

• • 

t t 

1 • 

1 1 

• • 

« • 

• to 

• •*•*•« 1 

III*!*** 

• •••*>•• 

• • * 1 * • 1 * 

• •«•*«»• 

1 * • i « « • 1 

• • i 1 « 1 1 * 

• * 1 I • ( • 1 

«»•«««•« 

• • 1 • < 1 • • 

* 1 1 ( • • • • 

o.S 

ddddddddy; 

'd.d^ 

'd'd'd'd'd'd'd'd^ 


O 3 


ooooooo.Soo 

'd'd'd "d "d'd "d “^"d "d 

P*a»i»i*Q«*P 

* Jm 


ft 

IN 




to S 

a 

o § 

oa 

CG^ 

o ^ 
ftS- 

« rt 

a 

to 

CO 


o o o 

'd'd'd 




i-> 

3 
o 
td 

■d 

i:i 
.§3 

(A O 
^ O 
03 O 
O ^ 

42(n 

pH »-H 


CO 

tyo 

fl 

■p- 

0) 

> 


o 

c 


CO 

bC 

.s 

a 

<v 

o 

& 

CO 

u 

o 

o 


SJOCJOq^OOO 


TJI IC 
(N IN 


g •.a 

o -Ph 


« 

CO ^ 

t£ P 
P ■*^ 

ft| 

O g 

® o o 

52 

g§ 
oo 


03 

a 

d 

fee 

CP 

o 


CP 

c3 

OP 

CO 


3- . 

a:^ 

O C3 

:S-C 
«5 " 

CO 


tOr^QCOSO-^INCOtJ'iOtO 

(NINCSINCOCOCOCOCOCOCO 


.^^t^oiN'ricr»050(NeO'»<»Oto 

iOOOi-c»-l.-Hi-l.-(rH(NIN<NNNiN 


SC 

"=3 

m 


to 

3 

rO 

o 

O 

M 

W 

d. 

a 

c3 

o 

w 


w 

o « 

’ 'M 

c-^ 

d.y 

k. 

•-"d 

■5 ^ 

to gQ 

2 

-a*' d . 

kjw.. 

Q... CO 

■< « 

■JS ?3 CO 

03.'=' 

P,?PO 










































































































GRAIN-DUST EXPLOSIONS. 




rO 

o 

>~1 


rO 

>0 


o 

o 

so 

cc 

"to 

•S 




00 

t 

CO 


H 

t-5 

pq 

■< 


m 

a 

B 

<b 


o <B 


C3 ' 


S S 


CQ 


ixJ £ 

a>.t3 


OJ 


PiHph ^i-,; 





X 

o 





p 










o 




S 

o 




G 

o 




tJO 

c 





G 

'S 

o 




G 

O 

p 




o 

G 




X 

t-i 




o 






HH 




«^-l 

CO 




o 

C3 




4-» 

IS 




V / 






C3 

U 

G 


, 


o 


c/3 



G 


G 


s 

O' 


o 


o 

p 


G 


(h 

S-H 

5s 


r> 


tJO 

P G 



.a 

o o 

CO 


G 

3 “ 



CO 

G o 

o 


CO 

a X 




o ? 



o 

C3 ^ 



G 

^ o 



8 




^s 

03 4-» 

•G tH G 




jsPp 



p 

•x 



G 

G 




o 

bX) 




bjD 

p 

bJD O 4^ 

C *-- T* 



■G 

•g G ^ 



s 

S tc © 




G G CO 



p 

**-4 

o 

P’5 G 

O es^ 







4-S 

-H G B 



CO 

^G_ 

P O 
.2 © p 



« 

K P^ 


C3 


O 

:3 

O) 

o 


o 

Ut 

CG 

G 

O 

u 

o 

{>> 

OP 

t> 

fl 

o 

o 

«4-H 

o 

tj 

G 

O) 

<»-» 

03 

X 

O 

G 

o 


o 

>. 

Cl 

r' 

a 

o 

o 

sH 

o 

G 

» 

ii 

« 

> 

o 

K 

o 

.Q 

d 

O 


o 

cG 

G 

O 

f-i 

o 

o 

G 

o 

o 


G 

o 

s 

o 


tA 

G 


e 

o 

o 

(-1 


G 

• pH 

O 

o3 

O 

’C 

■M 

o 

A 

« 

o 

c> 

G 

T? 

C w 
■2 G 

.2-^ 

PXo 

o5 


03 

. O lO 
p C 1-1 

oc o 

i-i a 

iC»OQ 
CO »o 

1 

G 


c 

H 

.<35 05 

e 

03 03 

03 03 03 

G 

G 

cc 

G 

a 


G 

c 

o 

!_ . 

P. c> 

—"2 

00 Pi 

ktS 

^C3 

s« 


p-g 

O • 

G^q 

=* s 

2.S 

O o 

pjj^ 

'2 >^'' 
•So 

>M» 

!G ^ • 

05 

L'!^ 

PL ts 

.1-^ t 

a, © 


Co 

•2 

o' 

HO 


s 

o 

O 

'S. 

•2 

So 

to 

5o 

So 

CO 

?i 

o 


*to 

CO 

'CS 

!>. 

<W 

02 


lO 

w 

hJ 

PQ 

<1 


CO 

ri*( 

(s 

c3 

a 

<v 

PI 


p 

G 

« 

a 

(s 

g3 


« 

bc 


"G o 

as 

'GxJ 

o o 

4-> 

(h U 

G ^ 

.H-> -f-> 

COCO 


w 

g 

05 

t 

o 

c/3 

o 


•2 

'o 

G. 

o 

o 


XJ 

o 


w 

G 

•2 

o 

Ih 

^ . 
4-**^ 
C/3 03 

G >1 


bi^ 


03 


- 2 
O B 

-o§ 

.a-p 

'^'Cj 
© C3 
G5Gi 

G2 c-> 

o 


a 

•2 S' 

■G =* 

^ CO 

L © 

G5d 

O .,>5 

S^iS 

© 3'to 

-je 

Gj ss a 

5 P’S 

-o -O CO 

ts o3 <““* 
03 P'g: 
-G 

«2 <, 


Gi . 
Pm 

te CO 
© 
§'G 

C © 

c“ 

G c/5 
x; G 

C/T iS 

tc o 
G J>> 

*c ^ 

o a 

© O' 

CO O 
so *SS 

« ® 
©^ 
PW 

p © 

^•3 

irt so 

G S 
C3 O 
ts M 
G Ps 
® *3 

^ a • 

o P Cs 

Pjs Q 

P CO >, 
k © © 
G > 

a 

apS 

•S 

G 

•G G c3 

0.2 cs 

gls 

CO ° a 

Gi^ O 

o 


p 

G 


-SE-.. 

Po © 
X 0.2 
W Ph 


© 

a 


gS8 


■ o 

: M 


lO 

tH 

c4 


G 

js 

o 


'O 

i-i 


© 

Pm 


Paj 

© 

n 

■G 

© 


IS 

o 

ss 

© 

p 

o 

o 

O 

d 




© 

© 

03 

©h4 

© . 

P©" 

05 © 

sa 

TO 

o « 

|d 

4-» ^ 

-a 

C3 4> 

&a 

.so 

©ui 

Sh »s 
JD 4^ 
4L> a> 
pG 'G 

p “ , 

05 J 

’-' ir<1 

2iiO 

>.o .. 

G •• 2 

?^ © s 

• •'S c 

® M P 

G u, 

P^O 


23 









































Table 6. —Series 6. Preliminary test with induction coil. 


c 


BULLETIN 681. U. S. DEPARTMENT OF AGRICULTURE. 




C 

(U 

P5 


W5 bl) 

«.s 

3 

2 

•Sp. 

I 

S'? 

il 

o C. . 

C3 C3 

>1 o 

o o 

1 P'S 

fs.2 g 

W o ^ 
c p 

g.SS 

■g pS 

[<.£3 bB 
<^>.■3 P 

2 i;.2 

.s-p ® 

>- OJ P . 

P.q— 

‘S P '^■p 
P 

os P'S 

-2 p 

PS 

O 03 


P 

p 

•4-J 

C3 

>■ 

(m 

a> 

CO 

o 


Ui 

fc£) C3 

a 

0) CO 


CO 


o 

o 


a 


'ooooooooooo 


V) ■ CO 
CO be fc£ w 
tee teP-tew 

f3.S p.5 fi 

‘C P'C P'S'S 
3 0 = 0 « P' 
o o o S o a» 

O CO O CO p 

g 3s 

-s P -S P “ 


E S » CO CO 

w ^ C3 ^ 5i? • 

O r; ^ T1 ^ n 

CSOso8|f:|!5SO 
CO CO CO CO CO CO^ 

•S .S .5 .S .5 .S .£ .£ .5 .S .£ .£ 

S O. s s s s s s s s s s 

.-H<Nr-cC<l.-i(Mi-(C<l>-i(N<Ni-i 


CO 

p 

'H. 

X 

o 

o 


S 

O 

4-> 

>4^ 

c3 

<N 


M c4 


CO 


Ul 

CD 

jJ P 

P> 

u h-5 

o _ 

So, 

§3 

oU 


+^pq 

3 .. 

.§.5 

"j: 

^ * 


CO PO 

S • 

®o .. 

Si:^2 


cc 






















































Table 7.— Series 7. Induction coil. 


GRAIN-DUST EXPLOSIONS 


X 

s 

o 


9 

T) 


® 

c 

o 


o 

o 


o 

& 

T? 

9 

sj 

9 

O 

ft 

CS 

be 

Ih 

C<3 

ft 

CQ 


c3 
*- XI 

CO 


X 

c 

c 


O) 

X 


u< 

becS 

C C4 
O) X 


eo 

s 


ft 


c 

o 


570000000 
£ 73'O-d "O t:? TO TO 

o I ’. '. '. '■ '. '• 

^2; :::::: : 


fi 

O 

1 

ft 

9 

O 




E i3 

o X 


,c 

f£ 


a 

C 

ft 

9 

9 

w 

o 

o 

03 

9 

fl 

ft 


3 

ft 

03 

O 

ft 

3 

C3 

-i-i 

OT 

3 

ft 

ii 

o 

■u 

cS 

> 

9 

c> 

<p 

a 


^ ^ O 4 ^ O 4 ^ O 4 ^ 
3 3”^ 3''^ 3'^ 3 
o< I ^ ^ ^ 


Qi 

a 

O' 

a 

oc 


. Q> 
> 

TO 

V. 

S • 

ftl-s 

(M ^ 

CC ft 

iS 


9 

a 


. IC 


o 

CO 


. 00 00 


s 

06 


a ? 


3 

CZJ 


50220 ®— 18 —Bull. 081 - 

































































Table 8 .—Series 8. Revolving damper. 


26 


BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 



. Tera- 

F.; hu- 

sr cent. 

carbons 

s. Con- 

<1) 

0) 

o 


CO 


t 

a 

3 

ft 

CO 

m" 

0 w ^ 

C>i Pi ^ 

• 00 5 

• 4-> 

O C3 

M 

o 

tM 

.3 


C9 

Pi 

3 

a 

® 


C3 O-rt 

CO w 

P 

■M 

CO 

o 

CO 

• 

O 

Cuo 

« 

'S“2i3-2ft 

2-:^ 

a> 

a 

s 

s 

f-4 

0) 


3 fl ® a ft 

3 3 
•t: o 3 

4Jft (£ 

6 

C3 

be 

c3 

CO 

a 

2 


cc2 m 

<1 

HI 

hP 




<3^ a;> 


w o o o o o 

ccc^ 


73 

C 

o 

c3 

t 

o 


K 


O 


M 


o 

ft 

£ 

c3 


C 

o 


c 

o 


x-|;| 

K 


w 

(C 

3 

ft 


fe 

3 


be 

o o.S o o o o 

-o TJ ^ "3 T) "3 3), 


O 

iz; 


o 

”3 


3 


£f 

ooo.Sooco 

-3'3'3ft'3'3’3’3 

4-i ‘ ‘ 

O 

;2; 


be 

_3 

553 

O 3 


be 


O 


o 

-3 


be 

3 


o 


oooooooooo 

'3'3'3'3'3'3'3'3'3'3 


O O 

-3-3 


<N 


ft 

ce 

c3 

ft' 

ft 


ft 


CO ^ CO ^ 

“ft 

ft«ft c3 

2ft 3=3'^ ?, 

' S 2 

S Sh ^ 

ce 3 
CQ (NCQP^ iM 


ft 
ce 
ce 
ft 

3 


be 

3 

ft 

o 

;2: 


bC 

3 


o 


c o 
ft "3 




o o o 
ft ft ft 


ff 

O 


c o o c 
ftft ft ft 


be 

.£ o 
ft'3 

o 

iz; 


3ft 

oo 


ce 

3 

ft 

® 

be 

;-i 

3 


be _ _ 

^ o o c o o 
ft ft ft ft ft ft 

o 

12: 


2.g 

^ S'O o 

pH »C 


be 
fi , 


X 

• ftft ft 

^ w Ti 

2 

* • 1 

* ^ • • 

• '2 


* • • 

1 ^ * « 

• -ft* 


ftft 

O’ M 


:ft 


o o o o 

C3 M’Oftftft 

.2S £ 

:2;aiP 


c 

ft 


o 

ft 


3 

c 


u 

s ^ 

3ft 

> 3 

ft 

"3 

3 

® O 

3l 

y. cj 


u 

^ c/ 

c3^ 

c3 
© O 


c3 


O O 


?3 

C 


3ft 
> 3 
2 

®ft 

3.3 

£.2 3 

32 O 
3 o 
X 3 w 


3 

be 


o 

ft 


^ 0C00000003 

3 ftftftftftftftftftS 

5 

P 


gft 
ft 


o a •*.= o 3 ■ 

B ssft H -q 


3 


—< ■(M«-'ri.':«3t''CC353—I <Mrb 


ub 


3-^ 

cs: 


o o o o 
ft ft ft ft 


3 

O 


° o 

! i:ftft 
;_o 
!P^ 


lO O t>. 00 Oi 


2a 




^ QO ^ 00 

; oc 


s 

00 


OJ 


c 

"-r 

Oi 


»C 

o 


























































































































































































GRAIN-DUST EXPLOSIONS 


27 


o ® ' 1:2 B S 

t- M tH 
O d; o (M 

c «®h§8^ 

g «J;-§ ®'L‘ 

“wft S'-a 

® ■t5rt'3+^ 

a 2 S ^ ® 

OtfljO w PvC o 

W 


I t 

*- nrt 

®I2 

|i. 

E-i. > a • 

» <D *H 

® ® 


® 

^ ® CO 

02 




a 


>> ® 
(1 


be 

■So 


fa 
3v® 

pH 12 ; 


XI "O 


be 

‘.S o 

52 ^ I ta 
« o *3 
'Ph 




be 

^000 
x’O'O’a 


o 

52 : 


XX 

c/2 C/J 

a rt 

XX 

xX ®x 

52 a m>52 
PhCOhPPh 


o 

X 


fa a 
00 


w 

o 


.000 
axxx 


-H es fo Hf< 

M cs es 


. o 

S” 

. 

a 


Kb 

CO 


i3 ® 

C 

fe s 

tin ^ 


gS 

03 ce 

-3 fa 

3 

El! 

05 


U 4 

to ® 
® & 
a 

03 


® 


S3 

Sw 

® E. 

pC3 y--s 

x^ ° 
cs 


E 

'C 

a 


c:> « 

ss 

X o< 

cs 


OTfa . 

S ° c 

•T^ O 
® © 
gas 

« a 
XX 

•Ht< 


i2 

a 

® 

H*-* 

c5 

cs 


^ lO 

cs c4 




CQ 


a 


Ui 

<0 

> 

0^ 

> 


«> 

3 

3 


a 

o 


.3 

® 

Ph 

M 

o 

•••4 

•d 

o 

^ ft 

^ • 

2^ 

C'^ft 

2 • • 

C w 

^ *M 

• • b 

4-> ^ 

93 

«o 

















































Table 9. —Series 9. Revolving damper. 


'28 


BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 


tn 

S 

d) 


2 n 

as 

4) . 

.ftp 

ft 

as-ga 

■e 

CQ CO 


t/i 


ft 

.£9 

3 

be 

a 

’•3 3 

ga 
0& 
^ft 
ft fl 
®.3 

ft k. 

o ft 
m 


w 

ft 

fi 

O 


w 

4-) 

g 

<4-» 

c« 


M 

<35 

CO O) 

•ai 

(lift . . 

I/I £3 o o 

-gSOQ 

op' 


Ol 

3 

o 


® 

cn 

ft 

o 


w 




be 

g 

ft 

o 

2 


o o o 
ft ftft 


ft. 

3 O 


be 

•S o 

ftft 


be 

o O.S o o 

ft ft ft ft ft 

* W 

o 

z 


be ' m be 
o.§c;^.So 

ftftft wftft 

- ' - o9 ■ 


O 


ft O 


CO 

§ 

<A <P kf,*J 
ft 3-- O 

c^PhPQIz; 


be 

0.2 o 

ftftft 

' 

o 

:z; 


ft be 
^.2 o o 

.ft ft ft ft 


® . 
«.2 o 

ftftft 

beV 


ft 

3.2? O 

p^wiz; 


ft 

3 


pc< 


be 

3 


ftp 

3 o 


CO be 

« 3 

toft 

c3 +j 
ft O 


be 

3 


ftp 

3 O 

piz; 


be 

.2 o 
ftft 
o 


be 

3 


o 

2 


ft 

3 

CL, 


o 

ft 


be 

ft 

o 

2 


ft 

3 

CL, 


o 

ft 


M 


be 


c« 


a 

CO 

3 

ft be 


.3 OOOO-^O.SOOOOOOOOrJ 
ft ft ftftft S Mftftftftftftftftft 


O 

2 


be 

3 


3 b 
ft3 O 

/!J2 


CO 
® 
ftft 


W 2? J5 CO 


3 


be 

3 

ft 

o 

2 


.2 ^ 
ft « 
oiS 
2fe 


be 

.So 
ftft 
o 
2 


Pft 

o 3 
22-« 


ft 

be 


CO CO 

W w __ __ W ® O . 

_coo^ftft3 *o^^ oooo 

S"=’.’a ^.SP.SPJS’i'Sl 

ft ' - - 


<N 


3.3^.3'55 a 
ft ft ft ft ft 
CO 05 


CO 05^ 


CO be CO 
® 3 ® 


be 

.2 o o 
ft ftft 

*j ■ ■ 

o 

2 


2 


.2 o.^ic oeft 

2 ^ (N 2 05 


3^. W 

a 

m 


ft _ 


3ft 

ij 

05 P=* 


a 

a 

3 

ft 

.M 

o 

3 

o 

..H 

8 


o o 
ftft 


o 

ft 


o 

ft 


«3 

O 


3 

O 


o 

ft 


ft 3 

GO 


o o 

ftft 


ft 

O 


o o 
ftft 


o 

ft 


o 

ft 


3 

O 


ft 

O 


3 

O 


o 

ft 


ft 3ft 3ft 

ooooo 


o 

ft 


o o o 
ftftft 


3 

O 


o 

ft 


ft 

O 


ft 

® 


:f ft 
ft 

® a 

3 w 
w bx) 

.2.S 

t'oH^OOOOOOOOOOOOOOOO 
o'^‘3'3'3'3'3'3T5'0'0'0'3'3'3'3'3 

5 • O. 

•2 w 


CO 

bjo 

a 

Ih 

3 

o 

o 

CO 


o o 


CO 

be 

3 

ll 

3 

o 

o 

CO 

ft 

3 

3 


o o o 


gftft g gftftft 

. o o 




‘.p5[s< 


® t. 

o ® a 9 o o 
ft ft ♦j S^ft 

:.a> 




co'^^oi^-oooio^cseo’^iccotx.oo 

^ ^ ^ ^ ^ ^ ^ pH pH 


05 


8?5 I?5?5c 5 c5?i 


® 

a 


.o 

SP 

.05 

3 . 


05 05 


2 8 


o 

CO 


CO 























































































































































































































GRAIN-DUST EXPLOSIONS. 


29 


« 

03 

C 

_o 

03 

>• 

b. 

o. 

CO 

XJ 

O 

O 


o 

rs 

3 

x: 

CO 


be 

O.S o 

T3 jzj-O 
o 
55 


be 

.S o 


o 

-a 


be 

fl 


o 

55 


CO 
(D 

Si 
beija 

^ fl, O.S ® 


/--V (H 

te ® 

o o< 

^ 9 
® S 

ii 

.2 M 


be 

3 

sw 

CO 3 

fa ft • 

2 

b.^ 

o 

®-3 O 

Z 

<M 


?s. 

hS 


05 


be 

a 

si 

o 

55 


a> 

S'-' 

c3 

o 3 . 

S *0 
_S o 

a> 


tc 

d 

si 

o 

55 


o 

o 

(b 

V 

Pi 

a 

C3 

-O 

CO 

« 

Si 


53 


COI-^ 


o 

-3 


O ^ 


CO 

C 

o 

CO 

_o 

ft 

« 

CD 

CO 

eo 


O o o 

■ 3 - 3-3 


3 

O 


be 

a 


S 

® a 
00-2 

Wft 

o 

* ® 
ub 


o o o o o 
^ X3 "d 


42 

ft 

a 

<u 


> f-< w 

I n n 


?? 


eo 


Sp 

Q ^ 

>o>^ 

.3 ® 
3.5 

a 5 

Sc.; 

L(j 
<* . 

an 

53 u 

wpq 

g« 

O b 

®.ii! 

.a .2 
S'S 


<:0 ^ 
jd’w • 
2 .-5i 


•g 

•-5«> 

« 

55 


>-1 

oo 


H 

Si 

pa 

<; 


CO 

5 

a 

<L 


CO 

C 

O 


CO 

O 


a< 

.s 

3 

o 

d 

a 

o 

a 

c3 

;h 


O' 

0^ 

CO 

CO 

O 

t-i 

U 


d 

s. 

o 


CO 

d 

o 


'O 

d 


03 

t-4 

a> 

d 

0^ 

C 


a> 

a 


®i2xJ A 
— 3 c 2 
Ai C S V 
.-. o ■ 


^ 2 
3XJ 


a> ^ 

.d3 


(- b, 

O 3 s *3 


Art O O 
*0 oo g yj 

52.3 2 ® 

5 ^ .2 

?3 CO ®.3 

ftg^ g 

P<’d O W 

<5 


<v 

ft 

o 

o 


03 

■S 

o 

c 

■4^ 

C3 

CO 

d 
3 
^ c 


ee! 

c ® 

.2'd 
*r ^ 

is 


OJ^J 

<» s 

00 A3 


be 


2 3 ® 

C C3 X3 
® oil 

® O 3 

to .2 2^ 

3 b. b O 

®.2 ?9 

aSto 

J, CO CO rtb 


3 

O 

"o 

3 

O 


3 

03 

o; 

fl 

<u 

Si 

a 

o 

O 

sa 2 

.2 » 
3 (S 


aii2 a 
o'S a> o 
®-2j3 43 

3 is CO CO 
m CT 

w^’b! 

b2 ® 

— bd 

a> P^otf 

^ d 

^ ox?*2 

o-S g ® 
bca ^ja 
>« o 2*^ 
o ® 3 u 
oAa « 


Si 

& 

bb 

03 • 


3 0 * 
w 


3 

.2 ® 

brt> 3 ® 5 
2 3^ 

53 a 

'SSg-5 3 

ft 


d +i> O *3 23 

Oi 

> Q 


o 

3.2 


b. 

3 

A3 

W • 

.3 =3 

«a 

3 be 

S ° 

cs a 
A 3 

3 be 
® 3 
A 3 O 
^A3 

3'3 

« rt 

> 3 
® 3 

A O). 

a"" 

O bb 
o d 

® a 


Hu¬ 

midity. 

Per ct. 

54 


Tem¬ 

pera¬ 

ture. 

O 

42 



gS 

.CO 

a 


CO 


a ^ 

rt. «5 

=’a 

w 


% 


Date: March 15, 1917. 

Observers: R. B. Fehr^ C. A, Nickle. 








































































Table 11. —Series 11. Double damper. 


30 


BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 


W 

C3 

a 




A ^ ^ 

© 




2 ' 

5 ® g o 
CO © © ^ 

'O fcN 

(t3 >> fc. o, 

°-S;2 

<5 H 


8’g 

cn w 


tc 

a 


o 

03 


5 £ c/5 

03 


a^J 

•Si'S “SI'S a 

Si2.2 " 3 

mE-'ccco H 


I/O 

p 

e3 


fi 

o 

-O 


*s—, 

3XJ 

.c-" 

M 


i-'fd 


" O 


& 

o 

’O 

d 

dJ 

CQ 


d 

o 

o 

CO 

d 

Uh 


d;dS 

c3^-2 • 

d^oS 
p d -d 
'O g 

•difitr-ss 
^ o ^-d 
M 02 


W 


'2 

© 


*2 


• 

O 

^ ^ 

S o-*« 

CO O 

^1^ A 

^ cis 

So 


2 

u 

'd 


© 

u 

d 

. 2 ? 

o 

a 

■1^ 

d 

« 

o 

ll 

v 

Oi 


d. 

P, 


•o 

a 

d 

w 


d 

O 


K 


O 

1 ^ 


00 


oc 


cc 

1^ 


o 

>> 

o 

> 

d 

o 

o 


W 


w 

d 

_o 

•.j 

CO 

> 

u> 

« 

lO 

X2 

o 


o 


a 

I 

>. 

m 


a 

u 

K 

a 

p 


<5 

S 


_ >-1 
d a> 
o D, 

^ a 

'm a 

OrQ 


•o 

2 


^d • 
d.o o 

w 


CO 

CO—* 

•C 

ti«« 

C3 O 

ll 

oz 


tc 

5 

JS 

o 

z 


be 

.a 

.d 

o 

z 


ts 

d 


to 

.a 

d: 

o 

z 


!d 

d 

a 


.d 

to 

OJ 

<d 

e 

be 

Im 

d 

P 


s> 

o 

a 

02 


bC 

d O 
'^O 

® a 

Zm 


be 
d 

za 


be 

.a 

.d 

(n 

.2 => 
ZP 


be 

d 

..H 

+J«d 

£ =3 
ZP 


bC 

.d 

(d 

.2 ^ 
Za 


bC 


(d 

d 


•So-i 

-G-o 

ap. 

02 N 


O 

Z 


fd 

O 


o 

•d 


o o o o 
■d "d “d "d 


d 

O 


o o 

-d-d 


o o o o 
'd'd'dd 


IM 


CC 


s> 

a 


g 8.1^2 8 ^i8itg8tJ.2A8g p*2?§ 

.e^ococoo 00 o'^oi oi d.cb.cbo^d.aa ..4.^ .da dd.d 

w 050i’^0»^0— 


1.49 







































































































GRAIX-DUST EXPLOSIONS. 


31 


.sg 

Ui 

'd 

S u 

Qi 

G 


5 o 
o ^ 

C - 


<X) 

G 


CO 

a> © 


o o a 

fSH 


d P 

CO 


, 


"y 

Pi 

a 

a 

73 

>4.^ 

CO 

CO 

•«o 

a 

a 

^14 

a 

§i2 

c3 G 

M 

© 

^ G 

a 

© 

•40 

.«o 

a 

© 

w 

w 

a 

© 

•4.0 

0)*^ S © 

£ 2 ® £ 

G 

© 

> 

• •H 

. G 

' u 

O 

G 

O 



pH 

a 



« 

l§ 

*^*d 

©*G 

C><.-| 

'C o 

"S w 


V 




■5 ^ 

03 o 
CQ 



ooooooooo 


»o to oo 


s? 


oc 

lO 


o 

"O 


o 

rs 


o 

'O 


o 

o o o ^ 
'O'TJ'O > 

a 


c — 


(/: 

t>C 

•S 

L. 

o 

o 

ai 


<v 


Vi 

TJ 

<S 

a; 

Cl 

d 

12: 


s- "■ 


t5 ^ 

_ o 
a> 

.s 


o 


9-^ 


-G 

® S3 

« ® 
t- 

S g 

as 


w ^ 

®s 

2 

° K 

aa 


c» 


CO 

<s 

.C 

CO 

e3 


o— o 
feSfe 

a a 

a 03 


(N 


wO wo 
® o'- o 

^ ^ t-l 

® 3 S 

w o- S, 

03 a 

'w'^ 

CO 


c/i O**^ 

® o'- o 

^ fc- ^ t- 

W Qi ^ 

cSg^^g- 

• 1—< 

w»-< w 

<N 


CO 

G' 
O ' 


-td' 

* 


a 
o 

52 ^ t-i’— tH 

g a a 

wrr O 'C 


a 

a 

© 


CO 


T-« CO »o 1^ c^ ^ 

lo o *o *o O ' 


) <N 

> o *—♦ 




00 O I »o 
1-H CO CO CO 

csc^cs^c4 


IQ ' »0 I ! »Q <0 
00^CS'^Oi‘O'^»O»O 
CO ’ ^ . »o . . 

. CS .04 . <M . C^ C^ 

C^ CS M 


CO 


* >i 

gS 

ai 


u 

© 


© 

4-» 

CO 

u 

© 

< 

rS 

<B 

<v 

Pi 


be 

O 

a 

SJ 

a 

m 


CO 

■$ 

a> 

hP 


ti 

a> 

> 

C3 

« 

> 


a> 

tse 

ii 


C 

c 

> 


O) 

X2 

P- 

a 

c3 

O 


pH 

• ® 

P^.2 
o Pi 




a® 

1^. 

O/y, 


® 

N‘-l 

S? •' 
.0.2 
■Ji-P 

iP (j) 

CO • 

i:^ 
c3 • 

.f.2pq 

>P ! • 

^•CH 

• • *13 *-< 

© M ® 

ti © S 
Q^O 


O 

































































































































Table 12 . —Series 12. Demonstration. 


32 


BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 


w 

a 

« 

ai 


u <t> 


bCfi 

'g-rSlli-d 

^« g'd 'u • ^ 

a* s *3 b o 

5 .0 &,« « o o 

H CCOQ 


I 

® & 

!> O 


■3 o 3 a • 

W fl O 
.§bc§^''o 

. -O CJ ^ 

2 c3 H'S 
® d S E f* 

^ 2 ; PLI 


p 


p 

o 

l-> 


p 

o 

o 

l-l 


E t 


p-^ a 

ella^a^ 

a®'® 

'S'o “ « ^"eS ^ 

Oi O CO CO 


o 

c; 


d 


a 

a 

CD 

•4^ 

05 


>> 

< 4 ^ 

a 


p 

o 






o 

e3 

> 

If 

e 

w 

.C 

O 


c 

O' 

> 

1=: 

o 

O 


w 


OT 

o. 

I 

m 


O OC' QO 

!£:•«*< 'T* 


-.f 

•.J" -rr 


05 

'T' 


<u 

c 


02 


X! 

c /2 

03 


OC 


05 

■*»< 


tX) 

p: 


o 


2/d 

o 

a 

cc 


&c 


o 


tc 


Uj 

3 

J=i 

+5 

o 

52 ; 


o 

dJ 


EQ 

b. 

» 

p. 

a 

d 


tc 

C 

s 

+J 

c 


Si 

cc 

a 


si 

VI 




® 

a 

c3 

o3 

a 

02 


o 


o ®* ® 
., >/p 
fc:2P 
d "P 

j7® o 
^ ^2. 
a o ■ 

g-cc 

CO 


23 

CO 


Cub 

c3 

ti, 

bi 

t 


3 

cp 

3 

P 

• 

w 

s 

0 

b4) 

• ■H 

23 

23 

d) 


4^ 


44> 

44> 

1 

p 

0 

C3 

0 

0 

• 

a 


> 
t—i 

Iz; 

Iz; 

• 

• 

C4 


H^iz; 


p ® 
o a 

Ha 

g p 

T 3 


fe3 

c 


c 

o 


o o 

-d-d 


c! 

O 


TJ 

(JH 


P 

23 

4.5 

o3 

o 

TS 

® 

•c 

Q 


d fc. 

23 O 

4.5 ^ 
c3 <0 
O > 

'-' a 

I" . 
IIS 

-P 



c/^ 

q;) 


tfi 

a 

o 

I-. 


.3 

o 


(h 

3 

o 

« 

(-1 

Q 


3 CO 

023 2 
(d^ 3 
-d^J 

> 5 ® g 3 

®.2 

.3-3 00^ 

.^§60 

S ;2'4;2: 


'!§ o 




CO 


lO CO 


I 


.iO 

.00 


10 o 

04 


00 00 


iO O iC o 

i-H CO »-• CO 


C5 O » 


CO 




gS S ^ 


a 






C4 


CS CS C4 C4 04 


























































































2.40 


GRAIN-DUST. EXPLOSIONS. 


33 


in 


o 

o 




w 

o 


O 

CO 

0^ 


£ 


o 


.s *> 

fcjD O CJ 

C3::: o 

o ^ 

T? o 

O ^3COC./COOCO 

t! cs J^TJ-g^o-g^Qj-g 

=:B § 

j^T3.5^ cJ a 03 g C3 

1*^. P ca 02 


"0 

c 

C3 


o 

05 C 

^ e. 


OJ o 


= — 

O S o 

g.^p 

m 


tf: 

C 

2 

-4-> 

O 


X 


CO 

o 

s: 

CO 

c« 

(CJ 

o 

tc 

Urn 

2 

(N 


O 


o 


g d c « 

S 

m 


tn 


A 

te 

rt 

CO 

S c o * 
S'd^ • 

4-^ • • « Cm 

o * • ^ 

b 


<4 • * i-H 


o 

'd 


P. . - 

PlrS^S ® 

" ^ — bo 

tH 


CS 

a 

w 


C3 

P 


bC 

.S o o o 

.C 'O'C'C 


i2 o 


v. 

® 

t/: 

03 

<« 

CM 


C3 

tc 


.— o C r; 
—- tJ-C! V) 
ci 
tc 

lO 


03 

a 

cc 


o 

TJ 


o o o 

'C'C'O 


?c 

o 


G> 

'd'S 

^'d 

c 

. 03 
O +J 
12; § 

®'? . 
s o g 
■Srt c 
.2 ^.-tc 


o o. 


I 


tC 

p 

® 

be 

k. 

C3 


be 

.a 

la 

o 


“ p 

o 

P IH 

° a 

Si 

CO,;:; 


CO 


CO o 

o 

CO £. 

c3 g 

ca S 

3 

CO 


2 

0) 

tJO 

(-1 

C3 


CO 

o 

x: 

CO 

c3 

td 


C 

o 

tM 

a> 

Cl. 

a 

C3 

-c 


o 

T? 


O 

CO 

cd 


cn 


.1'^ O 

sT'-' 

o oj 
d Pi 

M a 

®-« 5J 

(N 


O 


Ih 

o 

'S 

CO 

c 


CO 

4P 

a. 

a 

C) 

c3 

o 

CO 


00 


<M 


c4 


O Q 

■f »n lO »o 

e4 p 4 cs ci 


(N 

O 


• >> 


Cl 



, 

, 


c c: 


•n’ 


p H 


o 

P 

P 

a 

o3 

P 

W 

P 

cT 

® 

« 


kH 

® 

P 

« 

P" 

o 

• SP. 

U^ 

o 

Q 

« 


O 

o 

C3 

CO 


a> 

'd 

® 

O 


03 

> 


o 


o 


03 

a 


CO 


o Hs 

O •s 

u 

^ <t> 
C? C2 
tj'd 

'S ^ 
a wi 

p.a 

ai^ 

-fpi • 

.-U 

(m • 
C3 J 

O c^ 

t-'P c3 

P! P ® 

2 iSCO 

«cr_co 

fc>. ^ • • 

^ I * ^ 
^H ^ a> 


o ^ 

ft; 


t-i 
® 

o 


) 















































































Table 13 .—Series 13. Effect of relief valve. 


34 


bulletin m, u. s. department of agriculture. 


a 


X" 

p CD d 



X-J 

•x 

d <v 
o ..o 



o 

® 

Sjx: V 


S 3 

d 

p 

ft'co 

d 

. a 

p . 

a^ss 

..©•■a o 

3! "3 a 

3 ’3 ^ CO 

> 

•-X 

x-> 

o 

0) 

05 

CO . ft 

a R • 

ooo R 
•3 ‘55 ‘O 

® P 

d 05 

3 ^ 

P Lx 

•rx C> 

C d O 

R 3 § 'C ft 
'SiwoS 
t a .® * 

x-> 

O 

P 

«XX 

05 

^ R - 
©OR 

.Q ® ft 

°a3 
.2 0.? 

'umidity 

side, 72 


3 

CO H CO 


5^uQ 



w 

ll 

o 

> 

c 

o 

o 


c 


w 

a 

•2 

c3 

>• 

u 

a> 

c/5 

pO 

O 


s 

C« 

c 


O' 

a> 


h“ 


s 

H 


. o o 

e CO CO 


•00 


0) 

o 

a 

cc 


o 


M 

3 
P< 
esi 

a 

d 
® 
a 

?3 

Pn a 


!3 

rX 

P< 

c 

c3 

o 

a 

C3 

•I-) 

o 

o 


o 

a 

CO 


C 

c: 

IS 

•w 

O 

O 

V. 

‘0 


W CO 

CO bC 


•SI 

S.3c 

d d 

aw 

cod d d d 

■(.j d 

P X-5 


053 

^P o 


:z;co 

(N^ 



o 

4x! 

O 

a 

CO 


<v 

o 

a 

CO 


IV 

«> 

CO 

d 
a 

■ft 
'd 

^. 

a« a 
::.ai 

c3 p,: 


C/5 


tx 

O 

x-^ 

d 

> 

<!> 

3 

CO 

d 

:2; 

•d 

a 

c3 


0) 
3 

CO 

d 

d 
d 
_ 03 
w w ^ 

od o 

05 O o 
>M fcx 

p. 

a> •> 


CO 

3 

”3 

L. 

O 


0 3® 
-3 w CO 
(N . 

.. O 




Id 

(N 


CO 

3 

T? 

t. 

O 

(J3 

> 

o 

"o 

CO 

d 

+J 

3 


’3 

i 


tx 

.3 


o 


CO o CO a 

sd-^sa a 
ft a ftis 

C<|COfO<N 


•3 
d 
3 

CO 

0 ^ o o o o 

I • • • 

C3 


o o 
S fl 


rt rt 


o 


S 
a 

,C tx 

■wxi ®2 d 

§2'gd2 

W w O ^ 

YT a So 

Mt-ico 5C^ 


CO CO 
. <D OJ 

;(d<di2 

• CO 


COrt 

<p'^^ 

j2 ® 
CO ^ 
^ M 

d.2 

CO <N 


C 

O 


CO 

o a 


CO 

*s 

ft 

o 

;< 


ft 

TJ 

d 

d 

CO 

® 

a 

3 


w 


. CO 

» d 

d j-x 

'O ® 
^ -*-> 

<v > 

3 


(N 


CO 


'^:2: 


s ® 

R 


'Hi 

« d 

§a 

i^«<d 

d 31) a> 
a'd_: 3 3 

cg.as.^.a 

«a;5aa^°® ^ 

•3 O . 
ft3 o 

-I ;«?; 




4 W W 

^ d d d d 


CO 

3 

d 

d 

<x> 

05 

txx 

<N 

d 

2; 

d 

c 

c3 

R 

3 

O 

d 

05 

tx 

3 


o o o o P o o 
dddd '^dd 


• e-X 

. cs '• 

• 

• 

I CO 

* 

. CO X 

05 O •-I DJ CO • X* 



1 

1 

1 

• 

• 

( 

« 

< 

• 

1 

» 

« 

1 

» 

» 

t 

• 

* 

• 

• 

^ ^ x-l « ^ 

• 

1 

• 

< 

• 



O 

rf xt 


Q 00 Q CO »0 
SC »0 O O O O 


00 o ?o »o CO 00 

-X CS <- 


OO^ 

00 00 o6o 605C5C5^ 0505^05^0505 o o o o o o o 


ic <o 05 oc 05 
CO CO CO CO 


a> 


CO 

tx 


CO 

0 / 


CO 

p 
- o 

• S'S 

rt 
53 


o 

■ft 


CO 


CO 

O) 

a 

3 

5a 


52 O O 50 3 OS 

0.2 0-3 o-d o 
—’3t 3 ft'^X';::' 

- X ft 
® X O 


c« 

a 

,o 

w 

ft 

X 

os 


CO 

4J 

ft 

a 


02 


>. 

a 

a 


Date: June 9, 1917. 

Weather: Clear; mild: temperature, 64-77® F. 

Observers: R. L. Sackett, 13. W. Dedrick, R. B, Fehr, P. X. Rice, R. E. Campbell, J. Weaver. 





























































































































Table 14 .—Series 14 . Various cereal dusts. 


GKAIN-DUST EXPLOSIONS. 


35 



0 © 


tH ^ 

c/5 

a5 

u 


s 

0 

rv>* 

c /3 

2§ 

•—1 

as 


tuO 

a 

T) 


Cio « 
Xn ft 

^ o 
colz; 


GXJ IN 

c ® 

" ‘ ^T3.2 ^ 

" 0 

1 Sb«.2 . 

oiSd'^ 

:a Is 


c/; 

D 

O c/5 
S3 « 

S'© 

§ 


I’/) 

§ 

Oi 

o 

p. 

© 


k. 

© 

C3 


P- 

o 

02 


O—' > 

O C3 P 

fl rrt +i W 

O O ^ © gi'^ 
© ;c^ k. if o 
S o-o 03 a.-. 

<5o 1-; 


■P . 

■S'? d o 

P3 P 

O 




Hn,» 

0 


0 

t 

p 



■g 



p 

w 

d 

Hi 

«) 

t 

» 


Os 


W 

k. 

o 

© 

> 

P 

o 

O 


(Zl 

VI 

a 

p, 

I 

>, 

« 


Vj 

a 

o 


k. 

© 

VI 

Xi 

O 


o 


© 

« 


« 

k. 

© 

P/ 

a 

03 

« 


© 

© 

Pk, 


i«d 

w 


O 

00 


>> o 

0^3 

tM 

C3 


tjC 

.S O 

o 


Sp 

3 

Ph 


00000 
T? 'O 'O 'O 'O 


W) 

P 

2 

O 

;z; 


00000 
'O *0 'O *0 'O 


o 

(A 


5P 

p, 

2 

a 

02 


SP 

P 

P. 

2 

a 

02 


000 
"O "P "P 


000 

'O'V'C 


o o 
'pp 


W) 

.a 000 

,p p p p 


000 
p p p 


o o 
pp 


o o o o o .Si, 
p p p p P ' 


p 

p 

o 

fe) 

p 

p 


p 

o 

kH 

p. 

cn 


o3 


ip 
p 
p- 

pp bfl 
■ • k, 

cd 


TJ 

C 

c3 

CO 


a 

02 


ip 

p 

"o 

a 

02 


tc 

P 

2 

<4-> 

O 


00 .^ 

pp2 


00000 

ppppp 


ip 


__ o o o o o 

—ppppp 

a 

02 


000000 

PPPPPP 


bl 

P 

P5i 


P . 

O ■<-< 

>- 52 
pp 

CO p 

■k> kr 

■P O 

2 +j 

a 

r ^ 
s:ij 
p 

CO 


p 

p 

C3 

CO 

. 

S 

p k^ 

P§ 

CO k 

k/ P 

a^ 

S c3 

£; a 

p 


O O X ■ ' o 
P P 'g O P P 


d 

{_ 


. tlt3ip 
0003 
;zip?;p 


00000 
'O "O "O *0 *0 


oooocooooooo 

g ^pppppppppppp 


CO TT IC CO * 


OCOiO f-» CO TT iC 


O 


00 Oi O *-H (N 
I-H 1—I f-H CM IM 


d 

s 

. 0 ‘O »C Q 
g 0 0 CO 0 


0 

CO 

^ TT 

S 

kO 

».o 

0 

n 

M 

05 ^ 

.1-H <N 

ci 

CM CM* 

CM 

C4 


H 









( Nothing 











































































































































































Table 14 .—Scries 14 . Various cereal dusts —Continued. 


3G 


BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 


CO 

M 

a 

a 


'C 

a 


3 

o 


cn 

n 

_C 

03 


o 

VI 

Xi 

O 


w 

u 

o 

>> 

o 

y' 

3 

o 

O 


o 

tn 

VI 

O. 

pq 


O 

<4-« 

pq 


P5 

k. 

o 

P- 

a 

C3 

o 


•3 

o 

« 


■Ego 


c 

a 


’v a-o g< 

.2 a^ a 

8 o 2 m 
^00 

n 

® a> o «2 
O ,2 ^ Q 

Mil 

“ p 2 
o S M'S 


«■ Sf c «« 

^ C3 o 

a "'S'S 

§.Q !S =« 

a; >. tH 

O’F'C 3 
O & 

..ixT-g 
.2 ® S'O 

Wf, o OJ 
00 


o 

o 


U) 

fl 

3 

■tJ 

o 

:z; 

o' 

o 


VI 

a 

o 

CO 

O 

& 

X 

o 

lO 


to 

«G 

a 


fcx; 

.S o 

•M 

o 

:z; 


CO CO 

:: :3 
P.CU 
rj’ 10 


IZ> 

a 

feb 

o 


CO 

(-4 

CD 


CD 

u 



t- 

CN 


^ CO 
CO CO 
I I 

oc cs 

CS CO 


.0 


a 


co‘ 


lO 

CO 


CD 

M 

o 

a 

CO 

xi 

CD 

D 


CO • 
1:^ ^ 

QJ §-§ 
2; 02 


sti 

3 

p< 


1 

.23 

• CO 


CO 

tl 

«3 

3 

P 

: 3*3 

a 3 

; « P 

a 

CO 

a 

ft 

oc 

>o 

1 TJ< »o 


CO 


o 

'O 


w 

3 

Qy 

<N 


3 

o 

u. 

p, 

w 


C3 


u 

cC 

"fp 


C3C 

C<3 

I 


3 

o 


3 


ti 

o 
P.3 

a3 

3;z 


31 

o 


(I bn 

O"’ 


(N 

ec 3 


3 « 
O P 

11 

P'3 

£5 

c§ ^ 


CO 

p. 

a 

CD 

4-> 

o3 

O 

iO 


>0 

) Cvl 


»o 




u* 

CD 


CD 

CO 

Un 

CD 

« 


CO ^ 

fi 

2 • 

8w 

p . 

apn 

•^k CD 

^ ^ Q 

CD .-< 

^ fcH ^ 

a Spq 

30.. 

3.. . w 

CO 8 2 


t 


fc 





















































Table 15.— Series 15. Various cereal dusts. 


GRAIN-DUST EXPLOSIONS. 


37 


CO 

u 

C3 

a 

o 


o 

a 

c3 

ft 


1 

r_j 


tc 

G 

'd . 

O CO 

.«-tJ 

a 


^ ^ Me 

'0.2'd a 

3 “.2 C3 
CO CO IM 


a 

o 

-d 

o 

fl 

Ui 

G 

o 

Ut 

03 

o 


o 

o 

s 


a 

o, 

• fH 

CO 

o 

O 

a> 
£ o 


-d 

o 

^'3' 


o « 

O U 

«<5 


'd 

•F^ 

a 

d 

a 


d 

O 






o 

OJ 

> 

C 

o 

O 


W 


lO 


W) 

_G 

S 

o 


bC 

.3 o 

.d-d 

w 

O 


bO 

.3 o 

d:'d 

o 

a 


bC 

.3 O O 

^■dx) 
o 


bo 

.3 o d 

.ddd 

■4-J 

'O 


be 

.3 

w 

O 


o 

d 


bO 

d 

!d 

O 


o 

d 


d 
d 

52 M 

o (-< .3 

a 

f2 50 o 


.d 

CO 

03 


o 

a 

03 


^ Ph 


CO 

a 

O 

•"4 

o 

to 

dJ 

O 


o 

a 


■w 

o 

a 


<=^o 

a 

I 

CO 


« 

o 

ft 

a 

C5 

fi 


Ed 

d 

ft 


Ed 
d 

o 

^dd 

a 

CO 


d 

ft 


o 

d 


d 

ft 

+o 

o 

.2 

I 

CO 


C 

c3 

CO 


Ed 

/«—s 

•w 


o 

ft 


d 


d 


d 

CO 

o 

a 

OP 

a 

3 

tea 

ft 

CS| 


t3 

G 

Ah 



CP 

s 

rS 

C 

■w 

O 

O 

*1.. 

I 

{>• 


a> 


d 

qd 

-w 

O 

o 


bO 

d 


o 


be 

.3 o 


bC 

.3 d 


be 


o.d <» o o.: 


be 




o 

d 


o 'iS o 

Iz; ifta 


a> 

oi 

ft 


I • 

03 CO 
OP 
CO 

pH 

P c3 

fta 
”d 

s 

o cq 
ftt^-d 
“So 

- a»§ 


d 

o 

ft 

CO 


d • 
• 

d . 

fc- o 
d-ci 
d 
O' 


: d o 

. O fc- 

• ^ ft 

• ftco 

. co*j 

■ftd 

• d c 

: a ® 

. w 

CO 

■ w I-. 

^ d o 
d 

: 


•5 

Ah 


OiS 
I^Ai 



* * * 




; 



CO 

23 CP 



• • * 




• o 

• a 



* t 


• • j 




■ G 

; d 


6-2 

t * 


I • I 

* • CO 

! CO 

• -■ 




. .ca 

;d 1 

CO 

_ a 

« FS * 


:i2 

: 


• >.«✓ 

w CO 
^ CO 

Id 

be 

a 

'P rt 

G y 

! G^ 


5k O 

w 


t- o o o 


(M 


d dd 
o o 5 
b. p 

ftfto. 

CO CO ft 

d dd 

sse^ 

CO CO S 
-tJ C 

d d is P 


o 

a 


d 

o 

i-i 

ft 

d 


ft 
o 

(D 

d I-' 

d . o 

E-TJC! 
d*. 


O u 


3 

be ™ 
^*=1 
.^d 
«d 
cg^- 

W d 
CO 122 

t" G'-' 


cx 

.3 o o o o o o 

d d d d d dd 


o 


CZ ‘fh 
H C3 

oid 

•E.2 

CO fc. 

- d 


d 

feb 

d 

.2 

'C 

d 


d. 


. CO 

O fc. 


d 

'd 

& 

d 

u 

u 

XJ 

CO 

Ui < 


CO 

o 

CO 

c3 

tea 


tH 

3 
o 
tea 

o 

t-l *S 

3^. 

G 

^•G • 

sfei 

idd 

■•c >* 

'-a-9 


• M CO 


lO CD 


00 


Oi 


. 

. m. 

L 2.00 

IC 

O lO 

a 

io o 
THC<i 

(N c 4 

ft 

ft" 




0 >O’-^’»t<cDI^0iO‘^ 

t-h<MOIC^CSO|54COCO 

c4 c4 c4 cvi cs c4 csi ci (N 


t£) 

d.a 

' 4-? 

o 


XJ 

CJ 

‘G 

XJ 


o 


• • ♦ 3 3 3 fci 

w w 12 

• 3 u- 3 

• - ft5 

dd-d-d - Eds x 

1 • • cr O' O’ ^ 

; ^ be C’ 

; O'CO 03 

— O' 

! ^ 

; o* ; ^ 03 ; 

• • . Tf 1-H 

• CS q-H 


fHNfH 


• CO • • 


G • 

3 b 
3 
o 
'G e3 

d 

•• d 


6tB 


d (i 
O' ^ 


lO cp 

30 Oi 

PlO’^OOOiO^HC^cO 
•'I' O ^ 1-H »-H C^l (N 

00 


CO fo 

CO CO CO 


CO CO 

c4 (N 

ci cvi c4 

c4cocococococococo 

CO 

CO CO 































































































































































38 


BULLHTIN 081, U. S. DEPARTMENT OF AGRICULTURE. 


T! 

O 


C 

c 

C) 


eo 

"to 


to 

<SJ 

CO 

to 

c 

•<s> 

K. 

to 




00 




tc 

t-h 

w 

1-3 

PC 

<P 

H 


v> 

a. 

b. 

ca 

S 

o 


PC 

O 

•M 

.2 

'B 

o 

u 

'3 

o 


3 

3 

o 


_o 

;< 

‘to 

O 

‘w 

O 

3. 

fc 3. 

3* 

X 

O >< 

O 

o 

o 

<u 
£ O 

o 

b. 





o 

•to 

3 

,3 

M 


3 

c 


I- 


u 


w 

3 

_o 

Vj 
CS 

t 

X 3 

O 


I 

b. 

o 

>> 

a> 

> 

c 

o 

u 


W 


o 


o 

Ph 


« 

b4 

3. 

a 

ca 

Q 


b. 

ce 

Pi. 

tC 

r 

C4 

3 < 
PP 


.3 

to 

pb, 


O 

.2 

I 

CO 

to 

3. 


a. 

be 

b> 

3 


b£ 

3 

S 

o 


CO 


to 



• 1 

Pi. 

* • 

. &JD 

T^. 

• 3 

83 

e 

•A 

• 4-> 

VI 

• o 




•3 

o 

e; 


T) 

_o 

*3 

to 


a> 

>- . 

^ a 

"x o 

“^to 

3 

.. o3 


t^.a o 

3 C8to 
^ fcC • 


o 




w 

o 

o 

w 

C 3 

a 

. 

■3 ■« 

>.a 


S’^ 

to cJ 

osto 
3 o3 
erS 


be 

.acooocoooo 

totototototototototo 

^ .... 

o 


bc 

.a 

to 

o 


tol 

3 

Pi. 

"a 

a 

02 


•4 




Nothing. 




b 

3 

to 

c 

;? 

0 

3 flashes 

(damper on) 

no puffs. 











CO 











3 

3 . 











o 





to' 











3 
. 3 . 




V 


in 

o 









to 

a 





o 




’Z 


c« 





«»H 




Pi. 

to 





CO 




»o 

CO 


O 


lO 

Ub 


be 

.3 

to 

-bJ 

O 


3 

to 


o 

«-i 

I 

n 




W) * • * 


d 


S o o o 

CO 

to 

• 

to 

^ t5 'O 

» t 1 

:3 

• 

3 

o * • • 

Cu 


Ph 

* * * 

t * * 

to 


CO CO CO r< c 3 
*5 -bs .3.3 .3 c3 
3 3 3 (S S3 c3 O 

O O C b- b. b. 

b. t- b. be be be© 
C3 3.3v-.toto 3 

CO CO c^^^ 3 

iePito-g-C-C'J? 

. rrt 3 rrt to to *3 

• toco2r-c^.r.ra 

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Weather: Clear; no breeze; temperature, 67-64° F. 

Observers: R. L. Sackett, B. W. Dedrick,.R. B. Fehr, R. E. Campbell, H. R. Brown, J. Weaver, A. Kerstetter. 
















































































































GRAIX-DUST EXPLOSIONS. 


39 


DISCUSSION OF RESULTS AND CONCLUSIONS. 

SPARKS E]>^ITTED BY FOREIGN SUBSTANCES. 

^fany attempts were made, in both the preliminarv and the regular 
tests, to produce dust explosions in an attrition mill hy introducing 
with the feed various kinds of foreign suhstances, such as nails, small 
pieces of stone and flint, and matches, but not once did an explosion 
occur. ^ arious kinds of grain products, with different degrees of 
fineness, and both normal -and minimum moisture contents, w^ere fed 
during these attempts. Evidently, however, the intensity and amount 
of the heat generated by the sparks from these foreign substances w'ere 
not sufficient to ignite the dust, although an explosive mixture of air 
and dust may have been present, as manifested by the regularity of 
the explosions obtained by the electric arc under identical conditions. 
In rare cases, and especially wdth very low humidity and moisture 
contents, it might be possible for a nail or other hard substance to be 
caught in such a w^ay that a very long succession of sparks wmuld be 
emitted wdth sufficient intensity to cause ignition. The results of 
these tests, however, point strongly to the followdng conclusions: 

1. Sparks emitted by foreign substances passing through an attri¬ 
tion mill do not in general appear to be hot enough to ignite an 
inflammable dust. 

2. Nevertheless, to take care of the exceptional case, every ]ire- 
caution should be taken to keep all foreign substances from entering 
the grinding machines. 

NAKED FLAME. 

Oidy two attempts were made to obtain explosions by means of a 
naked or open flame, but both were entirely successfid (p. 11). Safe 
conclusions are as follow's: 

1. Naked flames can readily ignite inflammable dust mixtures. 

2. A naked flame should never be allowed in the vicinity of dust. 

CARBON ARC IN ATTRITION MILL. 

The summary of all results obtained with the use of the electric 
arc is showm in Table 16. It is to be noted that in practically two- 
thirds of the attempts wdth materials which gave explosions at one 
time or another, explosions w^ere obtained by means of an electric 
arc located near the grinding discs. In every one of the 201 explosions, 
except Explosion 3 of Series 12, it was necessary to feed the material 
in the amount of at least a handful to produce an explosion. Appar¬ 
ently, a fairly dense cloud of dust was required to produce an ex¬ 
plosion with even the most intense source of ignition available, the 
electric arc. ^riio following conclusions can be drawn: 

1. An attrition mill is capable of producing mixtures of dust and 
air wdiich can be easily ignited by a sufficiently intense source of heat. 

2. There is much less danger of an explosion, wdien the rate of feed¬ 
ing is less than the amount which the mill can take care of. 


Table 1G. —Summary of explosions in attrition mill (electric arc and foreign substances). 


40 


BULLETIN G81, U. S. UEPAHTMENT OF AGHICULTUHE. 


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GKAIN-DUST EXPLOSIONS 


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42 


HULI.ETIN 081, U. S. DEPARTMENT OE AGRICULTURE. 



CARBON ARC IN DUST ROOM. 


The location of the arc in the dust room, at the (mkI of the screw 
conve^'or, did not cause an explosion (Series 4). This fact, however, 
merely indicates that the many conditions involved in an exjdosive 
mixture did not happen to be met in this particular case. Probably 
the dust cloud was not dense enough. In any event, it would be well 
to draw the following conclusion, especiaUy in view of ])ast ex])losions 
in mills, and those obtained by the arc located near the grinding 
discs of the attrition mill: 

It is always very dangerous to allow an open flame (or any source 
of ignition) in the vicinity of a dust-laden atmosphere. 


EXPLOSIBILITY OF VARIOl S CJRAINS. 


The summary of all the explosions of various materials obtained 
with the electric arc (except those in the demonstrations. Series 5) is 
found in Table 16. From the explanation of the meanings of the 
terms of the fractions appearing in this table it would seem that each 
fraction ought to indicate the inflammability of the material. As 
a matter of fact, these fractions, especially those of the same series, 
serve as rough indications of the relative inflammabilities of the 
various materials; but too much stress should not be laid upon this 
point, as most of the conditions of testing were beyond control. Kela- 
tive inflammability can proj^erly be determined only by careful 
laboratory methods which control the many factors entering into the 
question. 

In view of the fact that the grinding of oat huUs constitutes an 
important part of the work done by attrition mills, it is interesting 
to note that oat hulls alone (Mixtures 1, 13, and 30) were not found 
to be very inflammable. Only extremely fine oat huUs, or those with 
considerable dust, were capable of giving inflammable mixtures, in 
spite of the fact that in series like 11 and 12 oat hulls were fed into 
the mill and recirculated continuously for several hours without a 
resulting explosion, except in the case of Explosion 3 of Series 12. 

A study of Table 16, together with a knowledge of the conditions 
of testing, makes possible the following conclusions: 

1. Elevator dust, flour, wheat scourings, and malt sprouts seem to 
produce explosions the most consistently. 

2. Oat hulls do not appear to give very inflammalde mixtures, 
unless they contain a cons^iderable amount of fine dust. 

3. Every precaution should be taken to remove dust as fast as it 
is formed, and to prevent it from coming in contact with any possible 
source of ignition. 


f 


GRAIN-DUST EXPLOSIONS. 


43 


STATIC ELECTRICITY IN ATTRITION MILLS. 

liepeated tests were made on various days, June 22, 23, 26, and 
July 1, 1916, to detect any charges of static electricity that might 
have been built up during the operation of the attrition miU. The 
devices employed for transferring the charge to the electroscope in¬ 
cluded the copper wire described in Series 10 (p. 16), and also a 
proof plane, consisting of a penny attached by sealing wax to a |-inch 
glass tube 10 inches long. The copper lead and proof jJane each gave 
good deflections of the electroscope when these devices were applied 
to bodies known to have charges of static electricity, and therefore 
it was certain that the methods employed for indicating the presence 
of static electricity were reliable. In the tests involving the use of 
the proof plane, it was held near the moving belt, or brought in con¬ 
tact with the frame of the machine, and then touched to the binding 
post of the electroscope, which was grounded by holding in*the hand. 

None of the tests run on the summer days mentioned, in none of 
which the humidity was lower than 70 per cent, indicated the slightest 
trace of static electricity during the operation of the attrition mill, 
with and without the feeding of various gi*ains. This result indicated 
either that no static charge was being generated or the machine was 
too well grounded, either directly or by leakage, to retain an}^ charge 
that might have been generated. 

By means of the usual voltmeter method the metal frame of the 
attrition mill was found to be well insulated as far as low voltages 
(110) were concerned. 

In order to test qualitatively the insulation and leakage for high 
voltages, one terminal of a Wimshurst machine was connected to 
the frame of the attrition mill. By means of the proof plane and 
electroscope it was found that the attrition mill was capable of 
retaining a slight charge for a few seconds after the charging wire 
had been removed. The indications of the very sensitive electro¬ 
scope, however, were so feeble as to lead to the conclusion that, 
while the attrition mill was fairly well insulated, its leakage (owing 
to the many corners and edges, covering of dust,' and also atmos¬ 
pheric moisture) and its capacity were so great that a considerable 
quantity of electricity would be required to establish a high potential 
on the frame. 

Further tests (Series 10)' on a winter day (temperature 42° and 
humidity 54 per cent) indicated the development of static electricity 
in the driving belts, due probably to the comparatively low moisture 
content of the air, but not in the frame of the machine. 

Safe conclusions from these tests are as follows: 

1. Any static electricity that may be generated in this particular 
machine is dissipated so rapidly by leakage, which is largely due to 


44 


BLILLETIN 081, U. S. DKPAHTMKNT OF AOKICULTUKE. 

the reljitively high atmosplieric huinidit}" of this region, that no poten¬ 
tial is built up in the frame of the machine. 

2. Should an excessive amount of static electricity be developed 
in a mill of any kind, jU’oper methods of gi'ounding the machine ^ 
will go far toward eliminating any danger tluit may he due to sparks 
from static charges. 

STATIC ELECTKKTTY AS CAUSE OF EXPLOSIONS. 

In 25 attemj^ts to ignite inflammable dusts with the sj)ark from 
an induction coil, not a single exjdosion was obtained (Series 6, 7, and 
12). From the fact that an electric arc would jiroduce explosions 
* under identical conditions, it would seem that the ])roduction of an 
explosion is largely dejiendent u]:>on the extent as well as the intensity 
of the source of ignition, especially when there is a high velocity of 
the dust past the igniter, as is the case in the attrition mill. The 
temperature of the electric arc is estimated at about 6,200° F., but 
laboratory experiments ^ have shown that certain dusts can be 
ignited at as low a temperature as 1,100° F. with a source of heat 
having a comparatively small area'. Consequently, great cai'e should 
be exercised to eliminate every possible source of ignition. 

Conclusions: 

1. It is comparatively^ difficult to ignite inflammable dusts in an 
attrition mid by means of static electricity. 

2. Nevertheless, every^ precaution should be taken to eliminate 
static electricity in the operation of anv kind of miU. 

EFFECT OF ATMOSPHEIUC HUMIDITY. 

The effect of humidity, both relative and absolute, upon the inflam¬ 
mability of dusts is not yet known, and can not be definitely deter¬ 
mined except by laboratory investigations under carefully controlled 
conditions. In the tests in the attrition mill the humidity of the 
atmosphere was always determined by^ means of a carefully cali¬ 
brated sling psy chrome ter. The relative humid ity^ ranged from 44 
})er cent to very nearly saturation, or 100 per cent, in the case of a 
steady rain. No deductions could be made as to the effect of the 
relative humidity on the inflammahility of grain dusts, for too many 
variable factors were involved. It is, however, of interest to note 
that in Series 3, during a steady rain, the regularity of ex])losions 
happened to be greater than in any other series^ This fact seems to 
indicate, at least, that a high relative humidity does not tend to 
decrease the inflammability of dusts, except in so far as the moisture 
content of the materials fed into the mill mav he considerably 
increased after a sufficient length of time. 


> References 38 and 39, Bibliography. 


2 Reference 26, Bibliography. 




GRAIN-DUST EXPLOSIONS. 


Conclusions: There is no positive indication in the ])resent series 
ot tests that the humidity of the atmosphere has any material effect 
on the inflammability of dusts in this region, where the relative 
humidity is usually above 50 per cent. 


Table 17. —Moisture contents of niaterials. 


Design i- 
tion. 

Material. 

■' 

Series. 

. 51 

11 

12 14 

15 



Per cent. 

Per cent. 

Per cent. Per cent. 

Per cent. 

A. 

Fine oat hulls. 

9. () 

9.9 

7 


B. 

Elevator dust. 

9. S' 




C. 

Oat hulls. 

8.9 


3. 2 i 9. 2 


D,. 

Flour (direct from store). 

14. 1 


I).. 

Flour (oven dried)..... 


9.3 

10 

S. 5 

F. 

Wheat scourings. 

’ 10. 4 

9.0 

r, 7 ' 

G. 

Corn.. 

9. 9 



I. 

Coarse floor sweepings. 

8. 0 


. I 

K. 

Conveyor mixture..!.. 

9. 0 



N. 

Fine oat hull dust. 



5. 2 1 


P. 

Barley malt sprouts. 



I '94 

4 0 

0. 

Malt sprouts. 



' 12 0 

3 5 

R. 

Brewers’ dried grain. 




4 7 





j 9 4 



lAlso typical of the first 9 series. 


EFFECT OF MOISTURE CONTENT OF MATERIALS. 

Table- 17 gives the results of moisture determinations made in 
several tests. Average samples were obtained during the feeding of 
the materials into the attrition mill, and were kept in carefully 
stoppered bottles. The method for making the moisture determina¬ 
tions was similar to that employed for coal analysis, in which the 
samples are placed in a constant temperature oven at 220° F. The 
crucibles containing the samples were weighed, by means of analytical 
balances, at frequent intervals of tune until the material was dried 
out, as indicated by two successive weights of practically the same- 
value. The percentage of moisture was then calculated on the basis 
of the original wet sample. Duplicate determinations were made in 
each case. 

The number of moisture determinations and the range of moisture 
contents were not sufficient to enable one to draw any positive con¬ 
clusions, but, in the case of oven-dried flour at least, a tendency 
toward more regularity and violence of explosions was noted. Un- 
doulitedly the same tendency would be noted in all grains if the con¬ 
ditions of testing could be properly controlled, and it would perhaps 
be advisable to determine the minimum amount of moisture to ren¬ 
der the material noninfiammable. For the present it seems that the 
following conclusions may safely be drawn: 

1. The less moisture a dust contains, the more inflammable it is 
likely to be. 

2. It is ])robable that for inllammable dusts there is a maximum 
moisture content above which the dusts can not be ignited. 


























































46 BULLETIN 681, U. S. DEPARTMENT OF AGRICULTURE. 

TESTS OF REVOLVING DAMPERS OR FIRE TRAPS. 

The te,sts with the revolviiit^ dampers gave the following important 
results: 

Table 18. — Tests of rcvoleiruj dampers or fire f.rn])s. 


Observations. 

Single 

damper. 

Double 

.damper. 

Explosions with dampers in 
service. 

29 

69 

Flashes past damper. 

6 

14 

PulTs past dami>er. 

0 

10 



Observations. 

Single 

damper. 

Double 

damixjr. 

Flashes at D. 


8 

PiiiTs at D. 


1 

Flashes at E. 

0 

1 

Puffs at E. 

0 

0 



These results indicate that the double damper showed no superi¬ 
ority over the single damper as a preventive of llame propagation. 
With both single and double 'dampers there were cases in which 
flames got past with enough force to shoot out of the peephole (B) 
for several feet toward the observer. The devices, however, were 
effective to the extent that no puffs of smoke and only one flame 
were observed at the end (E) of the conveyor. 



An interesting practical application of the revolving damper as a 
‘^hre trap^’ is noted in the following report of an investigation by 
R. L. Sackett: • 

A large milling company in Buffalo, N. Y., has placed its battery of attrition mills 
in a separate building of corrugated iron (fig. 5). 

Before the oats pass to the mill they have been screened and have passed a mag¬ 
netic separator, which removes splinters of wood, metallic substances, and other 
foreign matter. 

The material passes through the attrition mills and drops down toward the con¬ 
veyor below. 

The vertical leg below the mill has a 6-inch galvanized spout running horizontally 
through the side of the mill. On the end of this pipe is a flap valve with a circuit so 
arranged that if an explosion takes place in the mill the pressure will open the flap 
valve, break the electric circuit, which will in turn stop the motor which drives the 
mills. The pipe serves as a safety valve for the escape of gases in case of explosion. 

Below the safety valve is a “fire trap” or “damper,” consisting of four blades 
revolving on a shaft, within a casing, so designed that in case of an explosion the 
propagation of flame to the conveyor will be retarded or prevented. This damper 














































































































GRAIN-DUST EXPLOSIONS. 


47 


is similar fo those used in experiments in the special mill built at The Pennsylvania 
St^te ('jllege for the purpose of this investigation. 

This company reports that no damage has been done, and, so far as they know^ 
explosions have not been transmitted beyond the safety i)ipe and damper. 

The (loul)lo damper as installed in the present series of tests did 
not give the desired effect, probably because the two sets of revolv¬ 
ing paddles were too close together. If the flame can pass one set 
of blades, it is likely that it can pass an adjacent set of blades 
before it has been extinguished. It seems reasonable to suppose, 
however, that a sufficient volume or extent of passage between the 
two revolving dampers may cause the flame to expend its energy to 
such an extent that the second damper would be able to check it 
absolutely. 

The following conclusions can be drawn: 

1. A single revolving damper is a fairly effective device for pre¬ 
venting the violent propagation of flames, but is by no means an 
absolute preventive. 

12, A double revolving damper does not appear to serve the pur¬ 
pose of a fire trap any better than a single damper. 


RELIEF VALVE AND PIPE. 

Although the three tests with the relief valve and pipe leading 
from the hopper, of the attrition mill to the outside of the building 
showed that this device was not effective in preventing the propa¬ 
gation of flames, even past the double revolving damper, it is quite 
possible that a larger size of valve and pipe may aid' materially in 
accomplishing the desired result. The principle of permitting the 
immediate escape of confined gases that have just been ignited 
seems to be a proper one on which to base a preventive device. 

Conclusions: 

1. The relief valve and pipe as installed alone are not successful 
in preventing flame propagation. 

2. Tn view’of the correct principle involved, it may be worth while 
to try changes in the design and location of the relief valve and pipe. 

A study of the foregoing discussion of the tests performed at the 
experimental plant of the college may lead to the objection that not 
enough attention was paid to the quantitative side of the problem, 
involving such factors as the exact amount of grain fed hito the 
mill, the rate of feeding, the physical and chemical analyses of the 
material, the minimum temperature and minimum amount of heat 
to produce ignition, the velocity and analysis of the dust-laden gases 
at various points between the attrition mdl and the end of the con¬ 
veyor, the ])ressure developed by the explosion, the minimum 
humidity and the minimum amount of inert gases to prevent igni¬ 
tion of inllammable dusts, and the limits ol inflammability for vari¬ 
ous dusts. To such a criticism the authors would reply that the 


48 


lUJLLET'N G><1, U. S. DKPAHTMKNT OF AfiHICULTUKE. 

(|iiautitative side of the {)r()l)lein could l)e taken care of only by care¬ 
ful laboratory investigations such as are being conducted by the 
Bureau of Mines and the Bureau of Chemistry. The chief purposes 
of an experimental mill, such as that installed at the college, are to 
show that explosions can be produced in the grinding mill and ])ropa- 
gated a considerable distance, and to test various preventive devices 
recommended by manufacturing concerns or by the Government. 
Both of these purposes have been served to some extent. 

^Uthough it has not been demonstrated that static electricity, or 
sparks emitted from foreign substances, are capable of producing 
explosions in an attrition mill, it has been positively proved that 
more intense sources of ignition, such as an open flame or electric 
arc, can easily ignite dust mixtures, and that the resulting explosion 
can be propagated through fire traps aiid the screw conveyor. Con¬ 
sequently, the safest plan is to guard against every possil)le source 
of ignition. 

As to the second use, only three preventive devices have thus far 
been tested—a single revolving damper, a double revolving damper, 
and a relief valve. It woidd seem, however, that the present equip¬ 
ment would warrant further tests of preventive measures in coopera¬ 
tion with the Government. 

/ 

SUMMARY OF CONCLUSIONS. . 

The final conclusions reached after studying grain-dust explosions 
in an experimental attrition mill, together with the other results 
obtained by Government investigators, may be summarized as 
follows: 

1. Every effort should be made to collect and remove the dust 
from the grinding mill and surrounding atmosphere. 

2. In some cases it may be advantageous to use inert gases to 
decrease the oxygen content and thus prevent the formation of an 
explosive mixture of air and dust. 

3. Every possible source of heat should be eliminated where there 

* 

is any danger of having a dust-laden atmosphere. 

4. Every precaution should be taken to eliminate sparks due to 
static electricity.^ 

5. Greater use should be made of sheet iron on account of the 
very great danger from smoldering lumps of grain (Series 12, p. 17). 

6. Kevolving dampers, as installed here and elsewhere, appear to 
be of some value as preventive measures for the propagation of 
explosions. 

/. Ihe principle of the automatic relief valve should receive more 
attention as a possible remedy to apply for the partial prevention of 
the propagation of the flame. 


1 Jleferences 38 and 39, Bibliography 







APPENDIX. 

RECOMMENDATIONS FOR FUTURE INVESTIGATIONS. 

In closing, the authors desire to offer the following recommenda¬ 
tions for future investigations: . 

I. Laboratory experiments to determine the limits of inflamma¬ 
bility as affected by the following factors: 

1. Density of the dust cloud. 

2. Fineness of the dust particles. 

3. Chemical composition of the dust. 

4. Moisture content. 

5. Inert gases. 

6. Atmospheric humidity. 

7. Minimum temperature and amount of heat required for ignition. 

8. Sparks from metallic substances. 

9. Static electricity (not merely the voltage, but current measurements as 

well.) 

II. Field experiments on various types of machines handling dusty 
materials: 

1. Tests to prove that dust mixtures outside the limits of inflammability, as 

already determined, with reference to moisture content, inert gases, or 
atmospheric humidity, can not be ignited under the most severe condi¬ 
tions of ignition, such as those produced by an electric arc. 

2. Tests of various devices designed to prevent the propagation of explosions. 

RfiSUMfi OF SOME PAST EXPLOSIONS. 

The first large grain-dust explosion occurred in 1878 in the Wash¬ 
burn miU, at Minneapolis, Mimi. At that time the ‘Liew process’’ 
system of milling, in which the grinding of wheat was done by rnill- 
stones, was in vogue. It was assumed that, owing to a choking up 
of the feed spouts leading to the millstones above, one or more of 
the millstones became empty, and the running of the two stones 
against each other caused sparks, which ignited the dust in the 
conveyor boxes and dust rooms, causing an explosion in the dust 
room wliich destroyed the walls of the building. It is possible, and 
even probable, that the fire originated from open lights which were 
used at that time. 

Another very serious mill explosion occurred on June 24, 1913, 
when a feed-grinding plant in Buffalo, N. Y., was completely wrecked 
by an explosion, presumably of dust. None of the survivors of tliis 
explosion was able to give any information as to the cause of the 
mitial fire, but it is stated that without a doubt the explosion was 
caused by the ignition of feed dust. 


49 


50 


BULLETIN G81, U. S. DEPARTMENT OF AGRICULTURE. 

A i-ather curious explosion took place in a flour mill in Nebraska 
on Se])tember 22, 1914, in which the entire wall on one side above 
the second story was blown out. One end showed a bad bulge, 
but the roof remained intact, except that it sagged over the side 
from which the wall was blown out. Apparently the force of the 
explosion was exerted in one direction, or, rather, the wall on this 
side offered less resistance than the others. It is believed that the 
dust in one of the flour bins was ignited by a match struck by one 
of the workmen. 

On December 11, 1916, a large cereal mill in Ontario, Canada, 
was totally destroyed by an explosion and subsofiuent fire. The 
fire was started by an explosion in the feed-grinding building, and 
was ascribed to the ignition of feed dust in one of the grinding ma¬ 
chines. 

One of the authors witnessed several dust explosions in flour 
mills. Although these explosions were of minor importance, be¬ 
cause no serious consequences followed, the observations tend to 
give an idea as to the explosibility of flour dust, the conditions under 
which explosions may take place, and, in some cases, the cause of 
the initial explosion. 

At a certain mill the settlings .of the dust room, into which was 
blown the dust drawn from the middlings purifiers and from the 
exhaust off the millstones, were gathered periodically into a bin and 
ground on a small stone. This mixture was composed of very fine 
pieces of bran, fiber, larger pieces of endosperm, and a fine., impal¬ 
pable, starchy, flour dust. Often, when the spout became nearly 
empty and the pile above started down, the dust descended with 
sufhcient force to spurt out of the opening in the spout over the 
hopper, creating a dense cloud of dust. On one occasion an open 
light was close at hand when this dust fell, and an explosion fol¬ 
lowed. There were three distinct explosions or flashes of the burn¬ 
ing dust, one following the other at intervals of a few seconds. These 
explosions were succeeded by a faint crackling sound. Each suc¬ 
cessive flash was wider in extent as the dust spread and diffused. 

The fii'st enveloped only the vicinity of the spouts and millstone; 
the second, a still larger area; and the third, almost’the entire area 
of the grinding floor. Tlie first zone, composed of the heaviest and 
largest dust particles, burned the most slowly, as if partially smoth¬ 
ered; the next, more rapidly; and the last and largest zone, composed 
of the very lightest of the starchy particles in the state of greatest 
diffusion, burned most rapidly, and, consequently, with the greatest 
heat. This last explosion had more force than the others, and was 
more of the nature of an explosion than the other two. 

On another occasion some'purified middlings were shaken down 
from the side of an empty bin, and, coming in contact with the flame 


GRAIN-DUST EXPLOSIONS. 


51 


of an open lamp, burned with two distinct flashes, the second one 
spreading somewhat beyond the confines of the bin. These middling 
particles were too heavy to float far, and too large to burn rapidly. 

Only a few years ago a certain packer lifted the lid of a flour bin, 
and held a lighted match within the opening to see how much flour 
the bin contained. Apparently the flour had heen drawn down par¬ 
tially, leaving some piled up on one side. Set in motion by a slight 
jar, it fell, causing a rush of air and a thick cloud of dust, which 
was followed immediately by a long flame issuing from the opening 
in the bin. The current of air caused by the fall of the flour was 
evidently strong enough to prevent the flame from extending down 
into the bin; otherwise a disastrous explosion might have resulted. 
The flame burned the packer’s face and arms to some extent, and 
caused him to fall backward. In doing so, he let the lid of the hin 
fall, and thus cut off the flour dust inside the hin from the flaming 
dust outside. 

Tie conditions and circumstances existing just previous to each 
of these various explosions were similar in all cases. From such 
observations as were made the conclusion has been reached that 
only under certain favorable conditions will a serious explosion of 
flour dust occur. If the dust is very dense and confined within a 
certain volume, or if the particles forming the dust are very large, 
the danger of a real explosion is less than in the case of the very 
fine, starchy dust in less density, which may, however, burn very 
rapidly. The theory is that these particles of a fine, starchy nature 
must be separated by a layer or thin wall of air, and at the same 
time be near enough together to ignite each other. Dense clouds of 
dust, especially those containing coarse particles, are comparatively 
slow burning. 

A dust may also bo very fine, yet so widely diffused as to bo in¬ 
capable of ignition, even from an open light. The old-fashioned 
dust room, sometimes merely partitioned off with fine muslin or 
other clotli, constituted a dangerous source of lire or explosion, as 
the dust blown from machines was held more or less in suspension 
before settling, and, being for the most part finely divided, it would 
be all the more dangerous should it come in contact with an open 
light. 


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53 


54 


BULLETIN m, U. S. DEPARTMENT OF AGRICOLTURE. 


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